Materials for a Memoir 
ON 
ANIMAL LOCOMOTION. 
BY 
HARRISON ALLEN, M.D. 
Extracted from the “Report on the Muybridge Work at the Univer- 
sity of Pennsylvania—The Method and the Result 
PRINTED BY J. B. LIPPINCOTT COMPANY, 
PHILADELPHIA. 
18 88. materials for a memoir 
ON 
animal locomotion. 
HARRIS ON ALLEN, M.D., 
BY 
EMERITUS PROFESSOR OP PHYSIOLOGY IN THE UNIVERSITY OP PENNSYLVANIA. 
INTRODUCTION. 
The writer has undertaken, at the request of the representa- 
tives of the University of Pennsylvania, a series of studies on 
animal locomotion. The subject has been approached from the 
point of view presented by instantaneous photography, and has 
■been especially based on the results obtained by Mr. Eadweard 
Muybridge. He will also state that he is indebted to Professor 
Thomas Eakins for facilities afforded in studying the results of an 
experiment in the use of a modified form of Marey’s wheel de- 
vised by him, in photographing the action of the horse in motion. 
Many of the statements could have been deduced from data 
already accessible to the writer, but since he wrote the paper 
immediately after the inspection of the photographs his conclu- 
fions may be said to be based upon them. At the same time he 
has n°t hesitated to include materials not embraced by the photo- 
graphs. Whenever practicable the study of a given series was 
carried on at the same time that the animal itself lay dissected 
before him. For example, when studying the photographs of the 
elephant, he had the good fortune, through the courtesy of Pro- 
fessor Huidekoper, to dissect the limbs of an elephant. He has 
also dissected the horse, the ox, the raccoon, the sloth, the skunk, 
the Virginian deer, and the domestic cat. In the course of the 
35 36 
MATERIALS FOR A MEMOIR ON 
investigation Prof. Horace Jayne extended many facilities. Mr. 
Edwin A. Kelley has kindly furnished a carefully prepared list 
of the names of the quadrupeds and birds; this appears in an 
appendix to the report. Mr. Kelley also gave valued assistance 
in the dissections. 
To better inform himself on the subject of the gait of the horse, 
the author has observed the impressions made by the hoofs on a 
sand-beach. In this connection he desires to express his acknowl- 
edgments to Dr. M. H. Cryer for valuable assistance and sug- 
gestions. 
The great delay that would be occasioned in the preparation of 
this essay by subjecting every statement based upon observation to 
the test of anatomical demonstration, caused the writer to remain 
content with making many of the conclusions rest upon the evidence 
presented by the phenomena recorded by the photographs. He is 
aware that such conclusions are not in all respects satisfactory. 
The several heads under which the appearances are discussed must 
be looked upon as themes which suggest research rather than sum- 
maries of work already done. It is hoped that the notes may 
stimulate some of his readers to attempt to confirm the writer’s 
impressions and further to extend the application which can be 
made of the pictures to the important subject of animal locomotion. 
The “ materials” are so arranged as to make two main groups 
of notes,—those pertaining to the action of the limb when on the 
ground and those pertaining to the action of the limb about to 
leave the ground and when in the air. To these will be appended 
a short section on the human subject, on zoological considerations, 
and on flight. Occasional repetitions of statements of facts have 
been difficult to avoid in preparing the notes. The inconvenience 
arising from this defect has been in a measure overcome by the 
use of cross-references. 
The Use of Terms. 
It is necessary to propose the use of a few terms which will 
clearly express in a word a meaning which otherwise would re- 
quire the employment of a cumbersome phrase. The words flex- 
ion, extension, abduction, adduction, pronation, and supination 
imperfectly express many animal movements. Thus no adequate 
word exists for the movement of the hand upward and downward ANIMAL LOCOMOTION. 
37 
when the forearm is held in semipronation. Such a motion is of 
importance in describing the wing of the bird and the bat. The 
term Planation is here thought to be convenient, since it expresses 
the fact that the movement of the hand is in the plane of the 
flexor surface of the forearm. Planation includes both pronation 
and supination. Contraplanation as easily indicates a movement 
at an angle to the plane of the flexor surface of the forearm. It 
embraces flexion and extension, and is not especially demanded, 
except that a term which includes both flexion and extension as 
weH as abduction, as used in the sense of abduction of the thumb, 
may be acceptable. 
In like manner it has been found useful to employ terms for the 
different orders of the foot-falls. 
Synchiry indicates that the right and left foot of a single pair 
act together. Thus in the canter, gallop, and the run, the horse 
moves all the feet synchirally. The movement of the lower limbs 
in man is also synchiral. The feet may act alternately or together. 
In the strictest sense all mammalian limb-motions are synchiral, 
lf-> the right and left parts of a single pair move alternately, 
ns motion is at its maximum in the trot, and at its minimum in 
tie spring as performed by the kangaroo. The term is intended 
to apply to the act in which the feet succeed each other on the 
ground. The alternation of the right and left hind legs on the 
ground, while the fore legs are in the air, is a posterior synchiry; 
and in the same way the alternation of the fore legs on the ground, 
tie hind legs being in the air, is an anterior synchiry. The rabbit 
appears to resort to synchiry as an alternation of the walk even in 
ie slowest rate of movement; but, as a rule, it may be said that 
synchiry is an expression of a fast gait. 
th Uc^ry w°uld naturally embrace the movements in which 
ee act in combinations of hind and fore feet. But since these 
™~s are varied and important, it has been thought desirable 
s ltllte a positive term, and the word heterochiry* is proposed, 
ie walk, the trot, and the rack are heterochiral, since the fore 
°°t 18 flowed, not by its fellow, but by a hind foot. When the 
same^’^'6 assurn’ng the responsibility for this word the writer desires, at the 
me time, to say that it was suggested to him in a conversation with his 
mend, Professor T. N. Gill 38 
MATERIALS FOE A MEMOIR ON 
hind foot alternates with the fore foot of the same side lateral 
heterochiry occurs. When with the fore foot of one side the hind 
foot of the opposite side alternates, diagonal heterochiry takes 
place. 
In connection with the terms flexion and extension the following 
will be used: The movement of a limb against the medium in 
which the animal is moving constitutes the stroke. The move- 
ment in preparation of the stroke constitutes the recover. In the 
description of the “ hand-over-hand” movements of the sloth and 
the ape, the word “ flexion” has no place; yet the “ recover” is 
used in as exact a sense as in the movements of any other animal. 
When a limb of a terrestrial quadruped rests upon the ground 
it may be said to be “on,” and when not on the ground, to be 
“ off.” 
The term sura will be employed as a convenient word to in- 
clude the hind limb from the knee to the ankle. Crus has been 
retained so generally as a synonyme for the entire posterior ex- 
tremity as not to be available. 
“ Stroke” is the period of impact. It is included in flexion, and 
constitutes its first stage. “ Recover” embraces the last stage of 
flexion and the whole of the period of “ extension.” The terms 
“stroke” and “recover” are by no means the same as flexion and 
extension. They simply express certain phases of limb-function 
which are seen during the acts of flexion and extension. 
The support of the trunk begins in advance of the neck—viz., 
at or in front of the occiput (see p. 54)—and passes back to a 
point midway between the withers and the rump. In the camel 
the fore foot supports the trunk at a point as far back as the mid- 
dle of the posterior dorsal hump. In the same animal the pos- 
terior extremity supports the body from the dorsal concavity 
backward. (See p. 52.) 
In the Canadian deer (series 695, Fig. 1) and in the fallow 
deer (series 682 B, Figs. 2 and 3} the fore limb at one stage of the 
gait is directly under the trunk, and is the only support of the 
body. In Procyon (series 744, Fig. 3; see also p. 72) two limbs 
(the right fore limb and the left hind limb) are in the same posi- 
tion as the foregoing. In the sloth (series 750, Figs. 1, 6, 7, 8, 9, 
and 12; see also p. 78) the two lateral limbs are also the same. ANIMAL LOCOMOTION. 
39 
Ihe right hind foot of the horse (series 631, in the interval between 
11 and 12) is in the same attitude. (See p. 43.) 
herever occurring the position illustrates the tendency for one 
01 two feet of the same, or opposed sides, to support the trunk at 
some point between the vertical lines of the limbs. It is proposed 
to call such support central. Central support is opposed to the 
support ot the limbs in the extreme or forward motion of the fore 
limb and the backward motion of the hind limb, which may be 
called terminal. 
The Movements of Limbs. 
If a limb can be conceived moving in vacuo it can be at once 
understood that propulsion is impossible. For propulsion can 
follow only upon the initiation of an impetus, and this in turn 
only by the resistance of the limb against the medium in which 
e animal is moving, or, in the case of the terrestrial animal, the 
surface of the ground. 
-file resistance of the air and the water is so much less than 
t iat of the earth that the acts of flying and of swimming become 
radically different from those of walking, of running, or of any 
allied movement. In flying and swimming the resistance made 
iy the limb against the medium in effecting an impetus does not 
aiiest the movement of the pinion or the foot; whereas in terres- 
trial movements the instant that the foot strikes the earth the 
resistance is great and the arrest is complete. 
In the swimming-turtle the first stage of the recover drives the 
00t *u spite of the resistance of the water to the point at which 
.le Secontl stage begins. With some slight modifications the same 
|s tine of fossorial animals. Thus in flying, in swimming, and in 
owing the limb describes a continuous movement which unites 
le | °f the stroke to that of the recover. In the animal 
moving on the surface of the ground, the foot being brought to 
108 ’ an absolute break occurs between the beginning of the act of 
recover and its completion,—the time which would be required to 
escn e the interval and thus to complete the union corresponds 
t0 T}6 er* lat the foot is on the ground. 
le# rests on the ground until the trunk moves beyond 
tie point at which it can maintain itself. It is lifted at intervals 
" llch are dependent upon the momentum of the moving mass. 40 
MATERIALS FOR A MEMOIR ON 
One, two, or three limbs may be on the ground at the same time. 
The rates at which the succession of the foot-falls occur, in their 
turn, depend not only upon the rate of speed at which the animal 
is moving, but on the gait as well. (See p. 59 and infra.) 
The Positions of Limbs. 
In studying the motions of the limb of a vertebrate the position 
which answers to that taken by the salamander, when at rest, is 
assumed to be the best adapted for comparison. In this position 
the limb is horizontal to the plane of the longitudinal axis of the 
body. The ventre of the body and the ventral surface of the limb 
are on the same plane nearly. The limb of a reptile varies scarcely 
at all from that just named. When a terrestrial animal is erect 
the limb instead of being on the same plane with that of the body 
is moved a quarter of a circle downward. In the bird the posterior 
extremity when at rest is in the same position as the terrestrial, 
but the anterior extremity, in marked contrast to it, is flexed. 
When extended the extremity is thrown upward to a position as 
far removed from the horizontal position of the salamander in one 
direction as is that of the terrestrial quadruped in the other. 
In the movement of all limbs the directions in the main are 
forward and backward. The forward movement will be described 
as forward strain, and the backward movement as backward strain. 
Both the movements are oblique, but between them is a position 
which is straight. In the terrestrial animal this position may be 
said to answer to a line in the anterior extremity which lies imme- 
diately in advance of the withers and in the posterior extremity 
to the centre of the acetabulum. 
THE ACTION OF THE LIMB WHEN ON THE 
GROUND. 
Kinds of Work done by the Limbs. 
The kinds of work done by the limbs are two in number,— 
viz., that done by the fore limbs and that done by the hind limbs. 
The hind limbs are more powerful than the fore limbs, and in 
some animals, as the kangaroo and the jumping-mouse, are the 
main effectives. No terrestrial animal depends for support upon 
the fore limbs. When all the limbs are equal, or nearly equal, 
in length, the preponderance is still in favor of the hind limbs, ANIMAL LOCOMOTION. 
41 
owing to the fact that the great backward movement of these 
limbs on the trunk is made possible by the fixation of the bones 
to the pelvis, and through this structure to the vertebral column. 
Not only is this the case, but the hind limbs alone possess the 
power of propelling the body, so as to throw upon the fore limbs 
the labor of accommodating themselves to the rate of work of 
their more powerful associates. When an animal is moving at a 
high rate of speed, as in the gallop, the synchiral action of the 
hind limbs projects the body with such force as to compel the fore 
limbs to act simply as props, which successively carry the body 
forward until one of the hind limbs is again in position to give 
the body a second impetus. In proof of this assertion it is only 
necessary to observe that the greatest height attained by the 
trunk is that secured by the rump when both hind feet are off 
the ground. The statement generally made that the horse leaves 
the ground by one of the fore feet creates the impression that he 
gains the springing force from this foot, all the previous move- 
ments being in preparation for such a spring. In place of this 
statement another is here substituted,—viz., that the horse springs 
from that hind foot which last leaves the ground, and is “ off” 
from all feet when he simply relinquishes the support afforded by 
the last prop,—that is to say, the last fore foot. (See pp. 53, 62.) 
If the fore and hind limbs were based on the same plan, the 
motion of an animal would be either a series of springs—the two 
feet pushing against the ground at the same moment—or a series 
of steps, the two feet moving alternately. AYhile closely resem- 
bling one another, the two limbs are not on the same plan. If 
any motion takes place in the vertebral column at the time that 
the fore limb is moving, it is noticed that it occurs in the region 
of the neck. The scapula has a slight motion downward and 
backward. The trunkal motion for the hind limbs occurs in the 
region of the lumbar vertebrae, while the pelvic bones are fixed. 
The limit of the forward motion of the hind limbs is dependent 
upon the flexibility of the lumbar vertebrae. The limit of the 
similar motion of the fore limb is determined by the action of the 
muscles alone. The forward motion of the fore limbs is essentially 
the same in all animals, but the forward movement of the hind 
limbs is variable, because the lumbar vertebrae differ in degrees of 
flexibility. In clawed forms there is more lumbar flexibility than 42 
MATERIALS FOR A MEMOIR ON 
in the hoofed. In backward movements the opposite obtains, for 
in these positions the fore limbs can be carried back to a variable 
distance. In the deer and its congeners, owing to the great 
obliquity of the humerus, the fore foot can be brought to a point 
near the centre of the body, and the limb be vertical. (See p. 92.) 
In the horse the fore limb in backward strain is very oblique, 
and the foot, while well placed under the trunk, cannot reach the 
centre. In the baboon the fore foot cannot pass beyond a verti- 
cal line which intersects the trunk a little back of the shoulder- 
joint. The backward movement of the hind limb is nearly the 
same in all animals. The leg is always carried in a direct path, 
the limit of the movement being determined solely by the length 
of the limb. In a word, the forward movement is the less con- 
strained in the fore limb, while the backward movement is the least 
constrained in the hind limb. The most variable movements are 
the backward for the fore limb and the forward for the hind limb. 
The “stroke,” or period of impact against the ground, can be 
divided into three stages,—first, that of forward movement, when 
the foot rests against the ground, chiefly on the outer border (see 
p. 50); second, the vertical position, when the weight is borne upon 
the foot as a whole, or when the marginal toes are shorter than the 
third and fourth upon the central portion ; and, third, the back- 
ward movement, or backward strain, when the foot rests chiefly 
upon the inner margin. lam informed by Dr. M. H. Cryer that 
skaters invariably bring the skate “ on” the ice by the outer edge 
of the runner, and take it “ off” by the inner edge. Practically 
the same motion is seen in swimming for both hands and feet. 
The fore leg may be said to be thrust forward as the hand is 
thrust when used for grasping. The ground may be said to be 
seized by the foot and the body pulled up to the point of pur- 
chase. (See p. 52.) The hind leg (usually of the opposite side) 
pushes the hind part of the body forward at the same moment. 
As the fore foot passes its vertical it also would tend to push the 
body, and in this way assist the hind leg. 
In clawed animals the seizing power is carried to a high state, 
and in hoofed animals it remains at a low one. In all domesti- 
cated animals the pushing power of the hind foot is unimpaired. 
(See p. 92.) It is most modified in forms adapted for tree life, 
as the ape and the sloth. ANIMAL LOCOMOTION. 
43 
Motions essentially the same in all Quadrupeds. 
The motions of all quadruped animals are essentially the same. 
If a comparison is made between the dog and the raccoon, the 
contrast between the two forms is at first sight great. But if a 
careful analysis of the figures be made, it will at once be noticed 
that the points of variance are in the main due to the rate at 
which the animal is moving, the gait being the same. The flat, 
broad, yet exceedingly flexible foot of the raccoon is raised delib- 
erately from the heel to the toes, and at each stage of the strain, 
which is coincident with the heel elevation, the graphic expression 
of the pictures is totally unlike the short, decisive motion of the 
small and almost digitigrade foot as seen in the dog. (See p. 50.) 
But the order of the foot-falls is similar in the two animals. 
In like manner contrast may be established between the appear- 
ance of the foot as it is being carried through the air in prepara- 
tion for a stroke. When an animal is going at a high rate of 
speed the succession of the movements of the fore and the hind 
feet is altered. In slow rates the fore foot remains on the ground 
until the hind foot is in its turn lodged. For an appreciable time 
both feet remain on the ground nearly at the same spot. This 
position is well seen in the raccoon (series 744, Figs. 3 and 4) and 
in the baboon, as well as in the sloth (series 750). It affords a 
good example of central support. (See p. 38.) 
But in fast rates the fore foot has left the ground before the 
hind foot reaches it, so at no moment are the two feet on the 
ground at the same time. Flat-footed forms are capable of retain- 
ing the two feet on the ground at the same time without the sacri- 
fice of speed noted in the small-footed types, such as the soliped 
and the ungulate are compelled to submit to. 
In the raccoon the fore limb may be, in some positions, used as 
a balance to prevent the animal being toppled forward. 
Division of Parts of Limbs based upon their Movements. 
The limb is easily divided into two great parts,—that from the hi]) 
to the knee and that from the knee to the toes. The movements 
for the most part are the to-and-fro motion of that portion of the 
hind limb placed to the distal side of the knee, and to that part of 
the fore limb beyond the elbow. The muscles which move the 44 
MATERIALS FOR A MEMOIR ON 
toes and the body of the foot arise, or tend to arise, from the lower 
end of the femur, while those which move the leg arise from the 
pelvis in great part. 
In ungulates (series 682 A, Fig. 5) the entire foot may reach 
the ground when the animal is in rapid motion. So that the 
plantigrade expression is possible in an animal as far removed 
from that type as is the deer from the raccoon. The plantigrade 
foot is more flexible than the digitigrade; the distinction between 
the foot of the deer and that of the raccoon is great, notwithstand- 
ing the fact that the two feet may under some circumstances do 
the same work. 
At the end of backward strain of the hind limb the fibula will 
act as a check to eversion. It is probably one of the uses of the 
fibula to thus check the eversion and enable the same bone which 
affords surfaces of origin to the flexors and everters to slow down 
the action excited by these very factors. In mammals without 
distinct participation of the fibula in the composition of the ankle 
eversion of the foot is less pronounced than in those in which it 
is present. Thus, in the raccoon, the fibula enters into the joint, 
and eversion is evident. In those instances in which the ever- 
sion is well developed yet the fibula is rudimentary, the inversion 
of the knee is to a corresponding degree emphasized. 
Backward Strain. 
In the backward strain, as seen in the raccoon, the fifth toe 
leaves the ground before the fourth. The leg is always rigid, 
but the extent to which the limb lies back of the rump varies. 
It is less decided in the rack than in other movements, and is not 
so well developed in some animals as in others. This can be 
seen in contrasting the movement of the horse and that of the 
guanaco. For the animal last named, see series 743. 
When an animal retains the hind limb in backward strain and 
the fore limb in forward strain (the limbs being those of the 
same side of the body), the trunk on the same side is stretched 
out to the utmost and the genu-abdominal fold is made tense. 
(Series 680, Fig. 8.) When the backward strain of the hind limb 
is associated with the backward strain of the fore limb, the trunk 
is flexed (if such a term be permitted) and the folds just named are 
relaxed, and the creases of the skin on the sides of the trunk are ANIMAL LOCOMOTION. 
45 
disposed in a number of vertical lines. These creases are espe- 
cially well seen in the skin of the hog. (Series 675. See p. 93.) 
It is a noteworthy fact that the number and the position of 
the folds on the side of the hog are the same as those of the bands 
seen on the side of the trunk of the nine-banded armadillo, and 
it becomes an interesting matter for consideration whether or not 
the bands may not have originated in the same manner, and for 
some reason remained permanently. 
The position of backward strain, as already announced, is most 
variable for the fore limb. The strain is not, however, the same 
for all animals. The backward inclination of the humerus is 
greatest in the deer. It is pronounced in the other ungulates, 
excepting the giraffe. In the elephant it is scarcely discernible. 
(See p. 91.) 
It is evident that the limb that leaves the ground the last is 
the one which does the most work. This function probably varies 
at different times in the same gait, although there is nothing in 
the photographs which proves that such variation occurs. 
The amount of forward strain is also subject to variation. The 
deer possesses extraordinary power to throw the fore limb for- 
ward. The degree to which the facility to accomplish this act is 
carried is seen in series 690, Fig. 10. It is also marked in the 
raccoon (series 744, 745). The movement is much less marked 
in the horse and the ungulates generally. The deer exhibits a 
much larger anterior surface at the trochlear curve of the distal 
end of the humerus than does any other mammal which was ex- 
amined. In the deer the proportion is one-sixth of the shaft of 
the humerus, in the ox and horse about one-eighth. 
The sudden release of the backward strain, with eversion of 
the foot, must naturally tend to inversion of the knee; hence a 
simple torsion of the entire limb is effected. (See Torsion, p. 57.) 
The Manner of a Limb going “ ojf” in the “ Spring.” 
The nature of the “spring” is not made clear by all the photo- 
graphs. It is well seen in the horse (series 642), but in the dog 
the immense impetus which is gained by the “spring” would appear 
to be produced by a mechanism altogether inadequate to the end 
in view. The animal rises from the ground without the source 
of the necessary power to accomplish this act being evident. In 46 
MATERIALS FOB A MEMOIR 021 
the rabbit and the kangaroo it is easily understood how by the 
simple extension of the tarsus from an acutely flexed position, 
followed by the flexion of the digits, the body is sent upward and 
forward ; but the leg of the dog is already extended at the time 
that the “spring” is initiated. If, as is asserted by practical men, 
the horse is prepared for the “ spring” by the same succession of 
foot-falls as in the gallop or run, it is only necessary to look upon 
the last limb which leaves the ground as though it were engaged in 
preparing the leg for a recover from an average stroke. Since the 
eversion of the foot presses the inner border against the ground, 
the inner aspect of the limb at the knee is directed inward and 
subjected to strain. But the force generated by this strain is un- 
expended at the time that the foot is raised from the ground, so 
that the limb might be compared to a coiled spring which has not 
lost its power, and the stored-up energy is engaged to propel the 
body forward the moment that the inner border of the foot leaves 
the ground. While acknowledging that this is an hypothesis, it 
remains the best of the surmises which occur to the observer. 
It has already been seen that when the limb is in the position 
of arrest and the momentum carries the body beyond the perpen- 
dicular line it is thrown into “backward strain.” The instant 
that the strain begins the knee is seen to move outward and the 
hock to move inward. The parts of the foot below the heel re- 
main unchanged. The impact of the structures of the limb is 
thus impaired in backward strain. It is well known that in the 
pentadactyle forms the foot can be readily rotated at the medio- 
tarsal joint, and it is a reasonable assumption that it is at this joint 
that the distal part of the limb moves when the entire limb rotates 
outward. The femur, the bones of the leg, and the astragalus act 
as one factor, and the calcaneum and the remaining bones of the 
foot as the other factor. The socket for the proximal motion 
occurs at the hip, and that for the distal at the concavity of the 
scaphoid bone. There is also considerable motion between the 
calcaneum and the cuboid bone and between the calcaneum and 
the lower end of the fibula, if this bone is present, or with the 
outer end of the tibia if it is absent. Outward rotation of the 
main portion of the limb carries the calcaneum slightly inward 
by reason of the articulation between the calcaneum and the bones ANIMAL LOCOMOTION. 
47 
of the leg. Facets are here present in most terrestrial mammals. 
In the wombat the articulation is evident. It is present in a 
rudimentary form in man. 
The outer surface of the calcaneum of the bear is marked by a 
stout roughened ridge as it enters into articulation with the fibula. 
In the dog the surface is a small embossment, which probably is 
in contact with the fibula only at the time of the backward strain. 
In a single old dog examined the same ridge is present as in the 
bear. A similar ridge which developed under the stimulus of 
diseased action is seen in the skeleton of the tiger in the Museum 
of the Academy of Natural Sciences of Philadelphia. 
As the knee is rotated outward the outer border of the foot is 
slightly inverted. This disposition is opposed by the peroneous 
longus muscle which everts the foot. Coincident with the inver- 
sion the external crucial ligament becomes tense and the tendency 
to torsion is checked. 
The degree of outward rotation may be found to relate to the 
swing of the trunk. In the elephant and the camel the rotation 
is decided. In the goat it is apparently absent. It is less marked 
in the horse than in the cat. 
The Act of Turning Round. 
In the dog the act of turning is accomplished in the following 
manner: 
The hind feet remaining fixed, the body moves in front. It is 
thrown laterally on one fore limb, so that this member becomes 
more and more oblique to the line of gravity. At a time when 
a line drawn upward through the supporting foot will lie entirely 
free from the trunk the opposed limb has been placed in the line 
of gravity and a new support assured. In the raccoon (series 745, 
Fig. 17) the outer border of the foot is used for turning. 
Other figures which exhibit the phenomenon of the act of turn- 
ing are those of the dog, the horse, the tiger, and the lion. 
On the Effect of Positions of the Limbs on those of the Head, 
the Neck, and the Trunk. 
When the forward movement of the fore limb is the most con- 
spicuous feature of the figure the head is erect. When the posi- 
tion of backward strain is the most conspicuous the head is 48 
MATERIALS FOR A MEMOIR ON 
depressed. When the head is being erected the neck becomes 
convex in front and concave behind. When the head is depressed 
the neck is concave in front and convex behind. 
The movements of the head and mane can be satisfactorily 
studied in all rapid gaits of the horse, especially in the trot and 
the gallop. The mane flies backward as the head descends and 
clings to the neck as it ascends. 
The series of figures (649 A) of the trick-horse “ Hornet,” rock- 
ing to and fro, is of especial value in studying correlations of head 
position to limb movement. (See p. 93.) 
The Influence of the Body on the Shape of the Foot. 
In the goat (series 677) the outer parts are larger in Figs. 10, 
11, 12, and the inner are larger in Figs. 1, 2, 3, 4, and 5. 
In the goat the chief weight comes on the inner toe. In the doe 
(series 641) the two toes separate at equal angles to the axis of the 
leg. In the ox and the camel no difference is perceptible. Profile 
views of the lioness and of the elephant -are interesting in this 
connection. In the capybara the of the foot bears 
the weight. 
Value of the unequal Lengths'of the Tges. 
In a plantigrade animal like the raccoon the transition from 
the plantigrade to the digitigrade form will bring the short toes 
to the ground in the digitigrade position at times when the longer 
toes are yet on the ground their entire length. This position is 
well seen in series 744, profile, Fig. 19. As the foot passes still 
farther towards the tips of the larger toes the short toes leave the 
ground. At first they are in the axis of the metapodium, but 
afterwards they are thrown backward, and near the end of back- 
ward strain appear to be abducted. (See series of the raccoon, 
744, Figs. 9, 12, and 13. See p. 73.) 
On Obliquity of the Outer Toes. 
The oblique movement will be essentially the same in all in- 
stances no matter what the number of functionally active toes 
may be. A straight toe on the limit of the inner border and a 
deflected toe on the lateral aspect are always seen. In man the 
first toe is straight and all the others are inclined outward. In 
o 49 
ANIMAL LOCOMOTION. 
the goat, which has but two functionally active toes, the outer of 
the tw’o is deflected. 
The action of the toes must be studied in connection with the 
outward rotation. It is evident that the outward rotation must 
be at an end, or near an end, before the digits are taken from the 
ground. (See rotation in elephant, p. 90.) 
THE ACTION OF THE LIMB WHEN GOING OFF 
THE GROUND AND WHEN IN THE AIR. 
The first movement noticed in the limb after it is beyond the 
centre of gravity is the flexion of the foot. In the horse the 
hoof is thrown backward, and the under surface of the foot is 
directed backward, the heel being raised first. The sole is next 
directed upward. In animals possessing more than one function- 
ally active toe the toes are quickly adducted in the air, so as to 
offer the least resistance to the impetus of the entire body. Asso- 
ciated with the above, a pronounced flexion of all parts of the 
limb occurs excepting at the hip, where the movement is slight. 
A movement of the thigh towards the trunk is faintly discernible. 
In animals possessing long thigh-bones, such as the elephant, the 
movement is more decided than in hoofed animals. The same 
remarks are applicable to the movements of the humerus. The 
degree to which flexion is carried is more marked in the young 
than in the adult, and in terrestrial than in arboreal creatures. In 
the sloth (Choloepus) flexion is absent, the limbs being advanced 
by a swinging motion at the shoulder and the hip. (Fig. 11, p. 83.) 
In rapid gaits the unaided eye receives the impression of backward 
movement, but fails to be impressed with forward movement. It 
may hence be inferred that the former is a quicker movement 
than the latter. 
In the fore limb the last state of extension of the forearm 
answers to the action of the extensors of the carpus and of the 
digits. In the less delicate movements of the hind limb the 
muscles which extend the tarsus and the toes move the foot with 
less precision, and, it is likely, with less speed. The first stage of 
the recover is a deliberate act. Beginning at the toes, it ends at 
the hip. The second stage is quicker than the preceding and is 
more abrupt. Beginning at the hip, it ends at the toes. 50 
MATERIALS FOR A MEMOIR ON 
Proposition that the Foot strikes the Ground by the Outer Border. 
This movement most probably takes place in a constant manner 
in all quadrupeds. Huxley* describes the act in the chimpanzee 
as though it were peculiar to that animal. In the horse the 
movement is well seen in series 601, Figs. 3 and 4, left hind foot. 
It is also seen in Fig. 4of the right foot of the same series. The 
action is well seen in series 581, Figs. 10 and 11. (See pp,42,84,88.) 
The foot in all animals excepting the horse (and even in this 
single-toed form the movement of the foot is in nearly all essen- 
tials the same) is carried forward in sernipronation. After the 
foot strikes the ground on the outer border pronation begins, and 
is completed by the time the perpendicular line is reached. The 
foot leaves the ground by the inner border (the toes being succes- 
sively abducted), so that the pressure of the body is borne from 
without inward across the foot. (See Fig. 4, p, 73.) The foot 
is always everted as it leaves the ground. In a plantigrade animal, 
as the raccoon, the foot is carried during the last part of recover 
nearly parallel to the plane of support. In the rapid motion of 
ungulates and of the horse the foot may actually touch the ground 
nearly to the hock. (See p. 43.) In backward strain the hock or 
heel is gradually raised, and at the end of strain the animal is 
seen touching the ground by the tip of the inner functionally active 
toe. In the horse the foot leaves by the tip of the hoof. It is 
likely that the degree of impact of the outer border of the foot 
Avill be found to correlate with the degree of development of the 
calcaueo-sural joint,f since the weight must be carried along the 
outer border to the rest of the limb. At the end of backward 
strain the limb from the knee distally is in the same line. 
The entire series of changes from sernipronation to pronatiou, 
as studied in 'connection with the transfer of weight across the 
foot, is well seen in the tiger (series 729 and 730; see also p. 85). 
The Eversion of the Foot. 
The moment flexion begins eversion is established, and the limb 
becomes angulated outward at the ankle. The main axis of the 
proximal facet of the astragalus is correlative with the degree of 
* Medical Times and Gazette, April, 1864, 398. 
f A name proposed for the joint existing between the fibular process of the 
calcaneum and the fibula, or the tibia. ANIMAL LOCOMOTION. 
51 
this obliquity. The angulation is most pronounced in the horse, 
less so in the ox, and scarcely, if at all, in the hog. (See p. 55.) 
It is evident that the more the toes are separated the better the 
limb is supported. It would appear to be one of the uses of the 
digits that they are capable of moving so as to increase the width 
of the under surface of the foot. Such an increase of width en- 
sues from two causes,—first, from the pressure outward of the 
foot against the ground; and, second, from the traction of the 
digits by the action of muscles. The muscular action is most 
pronounced. It is well defined along the outer border of the 
foot. As the pressure, shifts across the foot from the outer to 
the inner border, the digits leave the ground and are lifted and 
abducted as they are relieved from duty. In the capybara the 
movement of abduction begins before the limb reaches the ground 
(series 746, Fig. 6). Just as the foot is lifted the inner border is 
turned outward and the sole is disposed to the air in the position 
of eversion,—that is to say, the sole, while directed outward, is 
so arranged that the inner border of the foot is directed down- 
ward and the outer border upward. As the foot is everted the 
toes become abducted. 
Eversion is well seen in the horse (series 622 and 633).' It is pres- 
ent, but less marked, in the deer (series 681). A good study can be 
seen in series 619. In the slow movement of the walk the feet are 
not everted at the moment of the removal of the weight, but after 
the feet are well in the air. This is especially noted in series 581. 
In series 594 the figures of foreshortening show that when, as 
in Figs. 3 and 6, the fore foot is lifted, the foot moves towards the 
median line, and when the hind limb moves it swings off from the 
trunk. It is likely that the greater width of the pelvis over that of 
the withers compels the hind limb to describe an excursus outward. 
That the amount of motion inward under the body is suscep- 
tible of modification is evident from the fact that among fast 
pacing-horses the feet are brought inward, in order to reach the 
same spot on the ground. Since the fore limb is the more mobile 
of the two, it is likely that in the process of adaptation* the in- 
* The word “ adaptation” is here used in the sense that a terrestrial animal 
possesses the power of modifying to a slight degree the movements of the 
limbs according to the character of the ground it is moving upon. (See p. 96.) 52 
MATERIALS FOR A MEMOIR OX 
ward movement is secured by the front limbs, and that the hind 
limbs remain the same. (See p. 42.) 
In the sloth the foot is lifted as well as swung. (See Fig. 11, 
p. 83.) It would be interesting to ascertain if the ape also lifts 
the limbs in swinging. 
All elements of the swing of the hind limb appear to be lost 
in the “jump” if the two hind feet act synchronously. 
In the camel the fore foot in backward strain answers to a ver- 
tical line which intersects a point as far back as the middle of the 
posterior dorsal hump, while the hind limb advances forward as 
far as the concavity between the humps. (See p. 38.) 
The Degrees made by the Limbs at the Extremes of Forward and 
Backward. Movement. 
The fore limb when at the extreme of forward movement pre- 
sents an axis which is very oblique as compared to the limb when 
in the perpendicular position. Again, when in the extreme of 
backward movement it is again oblique to the same perpendicular 
position. It has been thought of sufficient interest to record the 
exact degrees presented by these extremes of movement in the 
fore limb 'and to contrast them with similar movements of the 
hind limb. 
By the use of the word plus, or the plus sign (+), a deviation 
to the right of the vertical is indicated. In like manner minus, 
or a minus sign (—), indicates a deviation to the left. 
In the elephant (series 733, Fig. 13) the forward strain of the 
fore limb is 25° minus. The backward strain is 35° plus. In the 
hind limb (Fig. 10) the forward strain is 15° plus and the hind 
strain (Fig. 9) is 45° minus. In the lioness (series 728, Fig. 3) the 
forward strain is 50° and the backward strain 20°. In the hind 
leg the forward strain is 50° and the backward strain 50°. 
In the dog (series 707, Fig. 1) the fore foot at the end of back- 
ward strain, but as yet on the ground, is in an axis of 10° minus; 
the rest of the limb being 20° plus nearly. In Fig. 2, the foot 
having left the ground, marks 80° minus, nearly, while the rest 
of the limb remains nearly the same as when on the ground,— 
namely, 18° plus. In the hind leg, as in Fig. 5, the foot when 
at the end of backward strain gives an axis of 90° minus; while 
that of the metatarsus gives 10° minus; and that of the thigh is ANIMAL LOCOMOTION. 
53 
less than 5° from the vertical. In Fig. 6, the foot has left the 
ground, and with the metatarsus and leg to the knee, become 
deflected to 40° minus, while the thigh remains the same,— 
namely, less than 5° plus. In series 690 (Cervus dama, fallow 
deer) the anterior oblique is 140°, and the posterior 10°. 
The method here accepted of determining the degrees of the 
deflection of the different parts of the limb is sufficiently accurate 
for all purposes except in the case of the thigh, where the slight 
movement of the entire mass forward is an imperfect index to the 
deflections of the femur. 
It will be seen that the fore limb moves as a whole, while the 
hind limb varies in each'of its segments. It is true the fore limb 
presents an angulation between the axes of the digits in hoofed 
animals and the rest of the limb, but on the whole the limb may 
be compared to a prop. (See pp. 41, 62.) 
In a general way it may be said that the forward strain of the 
fore limb is parallel in the lioness to the forward strain of the 
hind limb; but the deflection of the hind limb in forward strain 
is two and one-half times greater, as compared with that of the 
fore. In the elephant the forward strain of the fore limb is 
greater than the forward strain of the hind limb by ten degrees; 
and the backward strain of the fore limb is ten degrees less than 
that of the hind. The general trend, therefore, of the two limbs 
in animals so remote as the tiger and the elephant presents con- 
trasts which in their way are as great as the anatomical peculiari- 
ties of the animals themselves. 
The correlations of these deflections with the trunk are doubt- 
less exact, but no systematic effort has been made to define them. 
A vertical line drawn upward through the foot and made to in- 
tersect the vertebral column might be made available in the for- 
mation of an index of importance. It is noticed that in the 
photograph of the lioness this vertical line corresponds to the 
second of the minute dorsal elevations. As a general rule, it may 
be said that the line intersects the vertebral column at a point 
answering to a distance of twice the breadth of the withers. Again, 
in the lioness the forward strain of the hind foot yields a point by 
which the vertical line can be drawn upward which intersects the 
vertebral column at the last of the dorsal marks. 
While the purpose of the forward strain in the claw-footed 54 
MATERIALS FOR A MEMOIR ON 
animals is to secure a purchase on the ground by which the trunk 
can be pulled forward, in the hoofed animals it exhibits another, 
—namely, to protect the massive head. (See succeeding section.) 
The following measurements have been made of the hind limb 
of the horse at end of backward strain in the rack, the pace, the 
trot, and the gallop : 
Back. Pace. Trot. Trot. Gallop. 
Time, 17. Time, 19. 
590, Fig. 2 591, Fig. 9 607, Fig. 16 609, Fig. 2 631, Fig. 3 
Foot, 2°-)- Foot, 0° Foot, 0° Foot, l°-(- Foot, 0° 
Metat., B°+ Metat., 21°+ Metat., 21°+ ,Metat., 30°+ Metat., 40°+ 
Leg, 40°+ Leg, 50°-f- Leg, 40°+ Leg, 40°-j- Leg, 60°-(- 
Extent of Forward Movement of the Anterior Extremity. 
The position of the hoof of the fore foot in forward strain 
varies with respect to the head in different ungulates. In the 
heavily-built forms, as the ox, it reaches the occiput only, in the 
Indian buffalo (series 701) the ear, while in the deer (series 688) 
it appears to advance even beyond the muzzle. (See p. 38.) 
This arrangement doubtless correlates with the massiveness of 
the head, when the fore limb comes to the rest beneath the head, 
as in the Indian buffalo and allied animals, and with speed, when 
it reaches the ground in advance of the centre of the head. 
The extreme position of the hind limb after it is taken off 
varies greatly, as indeed it also does in the limb just prior to its 
being lifted from the ground. 
The changes in the relative positions of the fore foot when off 
in the various gaits are important. In the dog and the doe the 
entire extremity is acutely flexed. In the adult deer it is ex- 
tended, as is also the case in the cat. (See p. 92.) 
The hind foot appears to retain its position for a longer time 
than the fore foot,—that is to say, in the fore limb the impres- 
sion is given that it is preparing to leave the ground soon after it 
passes its vertical, while in the hind limb the propulsive power 
is expended through the entire period of the “stroke,” and is 
as pronounced in the positions back of the vertical as in any 
other. 
The toes of the fore leg are flexed quickly, even in Echidna ANIMAL LOCOMOTION. 
55 
and Solenodou. So far as observed, all mammals flex the toes of 
the fore leg not only quicker than the hind, but more completely. 
The adduction of the toes after the removal of the weight of 
the body does not appear to be the result of a mechanical neces- 
sity, for it is subject to variation. It is less prompt in the fore 
limb than in the hind. At times when the hind foot is raised it 
tends to be abducted. An example of such retention is seen in 
series 594, Fig. 5. 
“ Slowing Up.” 
The descent of the limb must have an appreciable effect on the 
momentum of the body by presenting a surface of resistance to 
the air. This occurs in the manner made familiar by the bird in 
the act of depressing the tail-feathers to arrest flight. Great 
breadth of limb is therefore an unfavorable condition for rapid 
locomotion. The figures of a cat jumping, as seen in series 719, 
Figs. 1, 14, and 15, serve to illustrate the action. 
Position of Feet in the Last Stage of Recover. 
The feet in forward motion are carried in the position of semi- 
pronation during the first stage of the movement. This act is 
the best adapted to rapid action, since it presents the smallest 
surface of the limb to the resisting air. (See p. 49.) 
The Angulation of the Limb at the Ankle due to Direction of the 
Trochlear Axis of the Astragalus. (See p. 50.) 
Among the more pronounced correlations which exist between 
the contour of the limb and the deeper structures is the shape of 
the ankle. This is seen in the horse, the ox, and the hog. If the 
astragalus of each of these animals is examined, it will be found 
that the deflection of a line drawn through the upper or pulley 
surface forms an angle with the axis of the limb of varying 
degrees in the horse and in the ox, but none in the hog. The 
production of such a line in the limb whose leg- and foot-bones 
are in the positions assumed in life will show that the produced 
line of the surface in the horse intersects the metatarsus twenty 
centimetres below the proximal end of the bone, in the ox at 
eleven centimetres, and in the hog the axis is parallel with the 
tarsus. 56 
MATERIALS FOR A MEMOIR ON 
With these facts before us and the photographs examined, it 
will be seen that in the horse (series 576), the figure of the animal 
being seen foreshortened from behind at ninety degrees, the right 
hind foot is barely off the ground, and has not lost the position 
of the ankle when seen in backward strain. The produced axis 
of the leg will intersect the axis of the metatarsus at the position 
which corresponds to the production of the axis of the astragalus- 
pulley in the skeleton. 
In the ox (series 671, Fig. 12) the rear view of the left hind 
leg exhibits a totally different inclination. The foot is on the 
ground, but is about to leave it, and the produced line is much 
nearer the vertical. In the hog, as shown in series 674, Fig. 4, 
the axis of the astragalus as far as can be ascertained is also that 
of the leg. 
Training and Age as Factors of Disturbance. 
The difficulty in studying the actions of the domesticated ani- 
mals, especially of the horse, is owing in the main to the fact 
that the training to which the animal has been subjected modifies 
his movement. The draught-horse comes down on the tip of 
the foot instead of the heel, as is the case with other quadrupeds. 
In like manner the movements of the well-bred horse are influ- 
enced by the skill of the driver. In the gallop (series 624) it is 
evident that the rider is at fault in the management of the horse 
and disturbs his action. 
The trot and the fast gaits, such as the run and the act of the 
leap as taken by the horse trained for the circus, are unnatural, 
and belong to the class of the acts of the acrobat and the contor- 
tionist as seen in the human movements. (See p. 66.) 
The fact that the horse in racing can place each of the feet in 
succession in the same spot is in this relation unessential, and need 
not militate against any conclusion drawn from slower and more 
natural movements. The same remark is applicable to the fact 
that the fast horse, even in the walk, will place the hind foot on 
the ground in advance of the fore foot. 
The age of an animal will modify the movements. An old 
horse, as already seen, will place the tip of the hoof to the ground 
instead of the heel. In the same class the hind foot is advanced 
to a less degree than the young. In the colt, on the other hand, ANIMAL LOCOMOTION. 
57 
the forward strain is the greater. In the fawn, as already re- 
marked, the feet are more flexed than in the adult deer. An 
untrained adult feral animal is, all things remaining the same, 
the best form which should be taken for study. 
The weight of the rider being thrown forward on the fore legs 
may modify the gait. That the depression of the head in the 
forward movement of the legs is not dependent upon this circum- 
stance is shown in the figures of the rocking horse (series 649 A). 
An additional reason is here presented why, when practicable, a 
form taken for study should be feral. (See also remarks on the 
trot, p. 66.) 
Torsion of the Trunk. 
An animal in thrusting out a limb from the body may be com- 
pared to a boxer making a thrust with his arm. With each lunge 
the body is turned in the direction in which the lunge is made, and 
the impetus of the body-movement is added to the force of the 
blow. The twist that the body describes is checked by the plant- 
ing down of one of the disengaged feet. 
In the dog (series 707), while both hind limbs are off the ground 
and the body is being vaulted on the single fore limb, the entire 
posterior part of the body is deflected from the line of the main 
axis of the vertebral column. This motion is certainly dependent 
on the bending of the column, and is probably an example of 
torsion. If unchecked the motion would “ twirl” the body round 
on itself. 
But since the impression of the foot on the ground remains 
sharply outlined, it is probable that the “twirl” is greater in the 
proximal than in the distal joints, and is entirely lost by the time 
that the parts of the limb are reached which rest upon the ground. 
Thus the first impetus towards deflection, while originating in the 
vertebral column, is gradually transferred to that limb which at 
the time is serving as a prop, and the force of the movement is 
dissipated as the animal is carried forward. 
In animals possessing a rigid vertebral column the torsion 
which corresponds to the movement above described is not 
marked. But the disposition of the body to incline towards the 
side which perfects the forward strain—i.e., delivers the blow—is 
the same. Such inclination if unchecked would throw the body 58 
MATERIALS FOE A MEMOIR OjST 
off the straight line. The check is secured by the hind foot of 
the opposed side of the trunk coming on the ground. 
Series 707, Fig. 6, shows to advantage the disposition exhibited 
by the dog to twist the trunk during progression. This tendency 
is never seen in the finer varieties of the animal. 
The Act of Kicking. 
In series 658, which exhibits the kick of the horse, Fig. 1 shows 
the hind foot as not quite extended. When the kick is complete 
the foot is fully extended, as seen in Fig. 2 of the same series. 
The Position of the Fore Limb as to the Axis of the Trunk. 
An inclination exists for the foot to rest on the ground directly 
in the middle line of the body; but the foot is not brought to the 
ground in this position, but to the opposed side,—that is to say, it 
crosses the median line, and comes clown on the right side of the 
line if the left foot is considered, and to the left if the right side 
is considered. Such disposition is seen in the photographs of the 
dog (series 703, Fig. 2, and series 704, Figs. 5 and 6). The mo- 
tion described is best seen in the heavy type of animal. It disap- 
pears in the slender breeds, as the greyhound. The same remark 
is applicable to the horse, the crossing of the fore legs being seen 
only in the heavy breeds. 
The foot which comes to the ground at the median line will 
gradually be drawn to the lateral portion of the trunk, as seen in 
series 709, Figs. 4 and 5. In this position it leaves the ground. 
The prop movement must from this circumstance be less efficient 
towards the end of the vault than it was at the beginning. 
The crossing of the fore legs is admirably well seen in same 
series. 
Depression of the Heel. 
Complete forward movement of the limb tends to depress the 
heel, or, per contra, the forward movement of each extremity 
tends to draw the toes away from the plane on which they are to 
fall (series 601, trotting-horse). 
Inward Rotation. 
After the hind leg leaves the ground the limb is disposed to 
rotate inward, an act well seen in the horse and the elephant ANIMAL LOCOMOTION. 
59 
(Fig. 1). The ilio-psoas would have an apparent effect in prevent- 
ing this. It may be surmised that this muscle is a check to the ex- 
cessive inward rotation, or the muscle may not contract until later, 
and prove to be the chief factor in the second stage of the recover. 
(See p. 89.) 
Fig. 1. 
The figure is designed to illustrate the disposition for the limb to rotate inward. The inner border 
of the uplifted foot is oblique, and the leg is inclined towards the median line of the body. 
THE GAIT, OR THE SUCCESSIONS OF FOOT-FALLS. 
The order in which the feet comes to the ground would be a 
simple matter for study if the animal moved constantly at a given 
speed and gait. It is rational to assume that the movements are 
in part automatic, and the alternate motions of the right and left 
limbs, or the motions of both the left limbs alternately with both 
the right limbs, would insure a succession which could be premised. 
Motions are'as a rule rhythmical. One expects the serpent to 
undulate the trunk after a regular method, no matter what the 
speed of the animal may be. In flying and swimming, so far as 
is known, the movements are synchronous and constant. 
In the terrestrial movements of the quadruped, however, such 
is far from being the case. This is owing to a variety of causes. 60 
MATERIALS FOR A MEMOIR ON 
So far as the photographs in the Muybridge series are concerned 
the order of succession of foot-falls could have been improved— 
that is to say, could have been more accurate—if the movements 
in the record of each gait had been of exactly the same character. 
But in point of fact, owing to the practical difficulties surround- 
ing the subject, scarcely any two of the series begin and end in the 
same manner, nor has anything been recorded of the mental con- 
ditions of the animal, whether it was tractable or intractable, 
whether excited or quiet, etc.,—conditions so essential to the 
manner in which an animal may determine its motions. 
If it can be conceived that a perfectly tractable and composed 
animal had been moving in a circle, and the camerrn instead of 
being arranged in a line had been grouped in a central cluster in 
such a manner that they could secure correct pictures of the 
moving form in the same way as in the method actually adopted, 
it is likely that out of such an endless series a uniform set of 
pictures might have been secured which would have given com- 
pleteness of representative actions. It is reasonable to suppose, 
that the motion of a living creature, as in an unvital mechanism, 
when starting and when halting, may be different, and may present 
contrasts of the several parts to a greater degree than when studied 
at a regularly maintained rate, whether this be a high or a low 
one. 
Each position of the foot when three feet are down embraces 
the laterals with one of the opposed feet in addition. Thus, in 
series 738, Fig. 1, in addition to the right laterals the left hind 
leg is on the ground. But in none of the pictures were the left 
laterals detected in which the right hind limb was “on.” It is 
probable that the diagonal heterochiral grouping is a weaker form 
of support than the lateral, and is used as an expedient to shift 
the laterals from the right to left and back. 
In the use of the laterals, in all gaits the feet as they approach 
the end of the time at which they are “ on” are at the side of the 
trunk, while the feet in use as diagonals always remain beneath 
the trunk. 
The facts that no variety of the deer ever paces, that the mule- 
deer is the only variety that bounds,—i.e., that all the feet leave 
and strike the ground together,—that the Canadian deer soon 
becomes fatigued in the run, while this gait is the one longest ANIMAT. LOCOMOTION. 
61 
assumed by the Virginia deer,* point to the conclusion that 
natural gaits are correlative with structural peculiarities; and 
while quadrupedal movements are based on the same plan, they 
are subject to modifications in animals otherwise closely related. 
Gait may be modified, if not controlled, by the proportion of 
the length of the limbs to the trunk. The hippopotamus walks 
in perfect synchrony, so far as the unaided eye can detect. The 
fat pig can walk, but cannot gallop. The lean pig, on the other 
hand, can gallop. 
The fact that the giraffe is the only animal which is a pacer for 
both slow and fast movements cannot be easily disassociated from 
the great length of the limbs. 
The subject of the gait can be studied by observation of the 
animal as a whole, by numerical analysis of each foot as it is 
either “on” or “off” the ground, by numerical analysis of each 
combination of any number of feet, and by graphic analysis, by 
which means tracings of the feet in combination are secured. 
For convenience the subject is divided into the following heads : 
The Synchiral Gaits. 
The Heterochiral Gaits. 
Synchieal Gaits. 
The Synchiral gaits embrace the canter, the gallop, and the run. 
In the canter the momentum of the body is not sufficient to 
enable both the fore limbs to act as props until the hind limbs 
again are in the position to urge the body forward. Hence the 
animal is observed to come down upon a fore limb after being in 
the air. 
In the gallop the fore limbs act successively as props before the 
hind limbs come down. The run is the variety in which the 
limbs attain the greatest possible amount of strain, and in which 
the quick succession of the paired feet is absolute. 
The “jump” is an incident in the run. In jumping a hurdle 
the horse, in series 641, appears to come down on two fore feet at 
the same moment. In series 637 the horse comes to the ground 
on the left fore foot, and is instantly followed by the hind foot of 
the same side. 
* J. D. Caton, The Antelope and Deer of America, p. 270. 62 
MATERIALS FOR A MEMOIR ON 
In series 632, the front legs are “ on” and “ off” equally, each 
being “on” 2 and “off” 10 in a series of 12. While the hind 
legs are unequal, the left leg being “ on” 5 and “off” 7, the right 
is “on” 4 and “off” 8. 
The Gallop. (See pp. 41, 53.) 
In series 631, the fore feet are equal, being 3 “on” and 9 “off;” 
the hind legs are again unequal, the left being “ on” 3 and the 
right 4. 
In series 633, the feet are all moving equally. Each foot is 
“ on” 3 and “ off” 9. 
It will be seen that the fore feet move evenly for the front, and 
in two of the three series twice unevenly and once evenly. 
When the horse is going at a moderate rate of speed the greatest 
distance between any two of the impressions made on yielding soil 
answers to the interval between the anterior of the impressions of 
the hind feet and the first of the fore feet. When the animal is 
going at a high rate of speed the greatest distance is between the 
fore foot by which he leaves the ground on the leap and the hind 
foot by which he alights. 
In the canter the impressions made by the hind feet on the soil 
are in the same relative positions as in the gallop,—i.e., they follow 
one another at wide intervals. The fore feet, however, yield im- 
pressions which lie close alongside one another,—at about the 
same place. 
In contrasting the two gaits, it is evident that in the canter the 
hind feet act with such ineffective energy that the fore feet are 
compelled to follow each other in rapid succession to prevent the 
fore part of the trunk from falling. In the gallop the momentum 
of the body carries it easily over both fore legs, which can leisurely 
in succession act the part of vaulting-poles. 
In series 680, oryx, this is reduced to a minimum. In this in- 
teresting series all the limbs excepting the right fore limb are “on” 
and “ off” equally. Even in the right fore limb the departure 
from uniformity is not great, the order being “on” 4 and “off” 6. 
The gallop as well as other gaits show irregularity. 
In the fallow deer (series 682) the limb-movements are uniformly 
“ on” 5 and “ off” 11, except the left hind foot, which stands “ on” 
6 and “off” 19. ANIMAL, LOCOMOTION. 
63 
In the Virginian deer (series 683) the right fore limb is “on” 
and “ off” 13. The left fore limb is “ on” 9 and “ off” 15. The 
right hind limb is “on” 8 and “off” 16, while the left hind limb 
is “ on” 10 and “ off” 14. 
The interval is larger in the horse than in the ungulates. It is 
exceedingly small in the guanaco, series 743. 
Intervals between the Fore and Hind Synchiries. 
The horse may assume the lateral position in the gallop, as is 
seen in series 632, Fig. 11. In this figure, as well as one in series 
612, the animal uses the lateral position immediately after reaching 
the ground. That the assumption does not depend on speed is shown 
in the canter. In series 616 there is lateral support in twenty-four 
pictures, in series 617 two in twelve pictures, and in series 619 one 
in twelve pictures. 
The heterochiral gaits embrace the walk, the trot, the rack, and 
the pace. 
Heteeochlral Gaits. 
This gait has been especially studied from the figures of the 
series of the horse, the buffalo, the ox, the cat, and the raccoon. 
The Walk. 
In the study of the walk by the numerical method it is found 
that in the horse (series 579), while the hind feet are synchronous, 
the front feet are asynchronous. 
In the horse (series 574) the hind limbs are practically as asyn- 
chronous as the fore, while synchrony exists in the diagonal be- 
tween the left hind limb and the right fore limbs. 
In the same series of twenty-four pictures the following is the 
order of the feet that are “on” and “off:” 
Rh “off” 14, “on” 10. 
Rf “off” 9, “on” 15. 
Lh “on” 13, “off*” 11. 
Lf “on” 14, “off” 10. 
It will be seen that the right hind and the left fore legs are 
synchronous. 
Series 579. Eli “on” 8, “off” 4. 
Ef “on” 7, “off” 5. 
Lh “on” 8, “off” 4. 
Lf “on” 9, “off” 2. 64 
MATERIALS FOR A MEMOIR OjV 
In the walk of the buffalo (series 699) the order is as follows: 
Eh “on” 18, “off” 6; Rf “on” 16, “off” 8; Lh “on” 10, “off” 
14; Lf “on” 15, “off” 9. 
Nothing here is synchronous; the greatest discrepancy is seen 
in the diagonal and the least in the lateral feet. 
In the ox (series 670) the difference between the two fore legs 
alone is great: Rf “on” 11, “off” 1; Lf “on” 8, “off” 4. 
In the cat (series 720): Rf “off” 20, “on” 4; Lf “off” 15, 
“ on” 9 ; “ Rh « on” 9, “ off” 15 ; Lh “ on” 9, « off” 15. 
Here all feet are acting synchronously excepting Rf. Between 
the fore limbs there is the most marked difference. The left fore 
limb remains on the ground over twice as long as its fellow. 
In the horse (series 576) the diagonal Rf and Lh are “on” 8, 
“off” 4; while the opposed diagonal is Rh “on” 11, “off” 11 ; 
and Lf “on” 6, and “off” 6. 
The walk in the raccoon (series 744) shows that the fore leg 
moves slower than the hind leg. When the momentum of the 
animal is increased the fore leg attains the same speed of rapid 
change as the hind. 
The rate of the “on” and “off” of the fore feet is | to J, while 
in the horse (series 579) the rate is f “ on” to “ off.” 
The left fore foot is “on” the ground in 1, 2, 3, 10, 11, 12, 13, 
14, 20, 21, 22, 23, = 12. 
The left fore foot is “ off” the ground in 4, 5, 6, 7, 8, 9, 15, 
16, 17, 18, 19, 24, = 12. 
The left hind limb is “on” in 1, 8, 9, 10, 11, 17, 18, 19, = 8. 
It is “off” in 2, 3, 4, 5, 6, 7, 12, 13, 14, 15, 16, 20, 21, 22, 
23, 24, = 16. 
Thus the left fore foot is in the act of supporting and propel- 
ling the body for the same length of time as it is engaged in pre- 
paring for a second stoke. In the left hind foot the time of the 
foot when engaged in support or propulsion is but one-half that 
of the time when it is engaged in the air. 
Combinations in the Walk. 
Out of the number of combinations which it is possible to 
secure from the feet when on the ground the following is the 
arrangement most frequently seen in the act of walking: Two 
hind feet alone; two fore feet alone; two hind feet and two fore ANIMAL LOCOMOTION. 
65 
feet. The combination one hind foot and two fore feet has not 
been seen, though no reason can be urged for the non-occurrence. 
(See especially series 744.) 
Support of the Vertebral Column in the Walk. 
The lateral disposition of the feet in the walk supports the 
vertebral column at the ends, and the figure of the trunk and 
limbs compares with a truncated triangle whose base is on the 
ground. In the diagonal disposition the opposed feet meet at a 
point near each other under the centre of the trunk (when the 
other feet are “ off”), and the figure compares with that of an in- 
verted triangle whose curved base is directed upward. 
The animals which assume the diagonal central support are 
short-legged creatures. The best examples are the raccoon and 
the baboon. (See p. 72 and p. 75.) The approximation to it is 
seen in the capybara. It is never seen in the ungulate. 
The Trot. 
In the trot the succession of foot-falls is inclined to synchrony 
from the circumstance that the motion becomes more constant as 
the animal increases in speed. 
Thus, in the trot in a series of twenty pictures, 
Rh is “off” 15. 
“ on” 5. 
Lf is “off” 15. 
“on” 5. 
lii 593—another series—the order is as follows in a series of 
twelve pictures: 
Rh is “ on” 5. 
“off” 7. 
Lh is “ on” 9. 
“off” 3. 
Rf is “ on” 4. 
“off” 8. 
Lf is “off” 9. 
“on” 3. 
The left feet have moved in synchrony. The right feet show 
a disposition to remain on ground longer, and, therefore, are doing 
more work. 66 
MATERIALS FOR A MEMOIR OX 
In the trot ting-horse the fore leg which is about to leave the 
ground is apt to interfere with the hind leg of the opposite side 
as it is advancing to come to the ground. In order to avoid this 
mishap the animal is trained to lift the fore legs to a degree which 
is not required in the walk. The motions of the animal suggest 
that the act of trotting as developed in the horse for fast gaits is 
artificial and is not especially useful for studies in locomotion. It 
has the same value as the study of the motions of a “ trick-horse.” 
(See p. 56.) 
The Rack. 
That the rack is not a uniform gait is seen from the following 
statements ; 
In 594, in a series of twelve pictures, the animal stands on one 
foot alone once; is in the air in six; and on laterals in five. 
In 595, in a series of the same length, one foot remains “on” in 
three; laterals are “on” in six; and the animal is “ off” in three. 
The transition between laterals is well seen in the series 593. 
In the walk at least the transition between the laterals and the 
diagonals is effected by the hind limbs. 
In racking the impressions made by the hoofs on the ground 
are in regular alternation of front and hind feet. 
Pacing in the horse is a delicate motion, since any irregularity 
of the ground interferes. The giraffe is a natural pacer. The 
pace is often accepted by the dog. 
Transitions and Contrasts of Gait. 
The walk is the basis of the trot and the amble, which is in- 
deed nothing but a running walk. The gallop leads to the run. 
The run may be called an extended gallop. The amble and the 
rack are trained forms of the gait. The walk often breaks 
directly into the amble, and this into the gallop. 
The difference between the trot and the pace, as noticed in the 
effect the positions of the limbs make on the eye, is but slight. 
In series 602, Fig. 4, the fore and hind legs on the right side 
are both in forward strain. The fore leg comes down first, and is 
instantly followed by the hind. If the two had come down to- 
gether, we should have had the initial step of the pace. 
The trot and the walk are closely allied in all essential particu- 
lars. The manner in which the imprints of the feet are made on ANIMAL LOCOMOTION. 
67 
the ground is in both gaits the same. The front and hind feet of 
heterochiral pairs impress the ground at the same places. The 
intervals between the sets of heterochiral impressions are in the 
walk about thirty-eight inches; in a small horse they may be 
twenty-five inches. The contrasts between the figures in the 
photographs of the horse at the walk and at the trot are very 
pronounced in the profiles. (See series 584 and 601.) But in the 
foreshortenings the two gaits present appearances which are very 
similar. The reader may compare Figs. 4to 8 with profit. 
The trot and the walk are both heterochiral, and vary in the 
manner of lateral or diagonal positions of limbs. 
The chief difference between the impressions made on yielding 
ground of the feet in the trot and the walk is seen in the relative 
distance between them. The impressions are much farther apart 
in the trot than in the walk. 
Gaits are more variable in the slow than in the fast varieties. 
This is inevitable, since the fast gaits depend upon uniformity. Dr. 
Cryer, in conversation with the writer, states this as an impression. 
The Laterals in the Walk and the Rack contrasted. 
The lateral position as seen in the walk is essentially different 
from that seen in the rack. In the walk the fore foot is in for- 
ward strain, while the hind limb is in backward strain. In the 
rack, the fore foot being in forward strain, the hind foot is in the 
same position, so that the limbs are parallel to each other. 
In Procyon (series 744), the diagonal heterochiry shows that the 
fore and the hind leg, say of the right side, are both in forward 
movement, while the fore and the hind leg of the left side are in 
backward movement. 
In lateral heterochiry the disposition is reversed: when the 
fore limb is in forward movement the hind limb of the same side 
is in backward movement. 
The graphic method of analysis embraces the following consid- 
eration : The essential lines in a given movement have been drawn 
and arranged in the same order as in the photographs. (See series 
577.) As the walk is the most complicated of the gaits, it has 
been selected as an example of this method. The advantage is 
evident, for the observer is relieved of the action of but one pair 68 
MATERIALS FOE A MEMOIR ON 
of feet. The eye can pass easily from the combination of left 
hind and right fore feet—as in the line to the left—to that of the 
right hind and left fore feet of the lower lines to the right; and 
the plate itself being before the observer, the study of the suc- 
cession of foot-falls becomes an easy matter. 
The Graphic Method op Analysis. 
The Limbs of the Horse at a Walk in Diagonal Heterochiry. 
(Series 577. See pp. 64, 67.) 
1. 
Eh “off.” Lf “ on.” 
Lh “ on.” Ef “ off.” 
2. 
Kh“on.” Lf“on.” 
Lh “ on.” Ef “ off.” 
3. 
Eh “on.” Lf “on.” 
Lh “ off.” Ef “ off.” ANIMAL LOCOMOTION. 
69 
4. 
Bh“on.” Lf“on.” Lh“off.” Bf“on.” 
5. 
Bh “ on.” Lf “ off.” 
Lh “ off.” Kf “ on.” 
6. 
Kli “ on.” 
Lf “ off.” 
Lh “ on.” 
Kf “on.” 70 
MATERIALS FOR A MEMOIR ON 
Bh “on.” Lf “’off.” 
Lh “on.” 
Bf “on.” 
8. 
Eh “ on.” Lf “ off.” 
Lli “on.” 
Bf “ on.” 
9 
Bh “ on.” 
Lf “ off.” 
Lli “ on,” 
Bf “ on.” ANIMAL LOCOMOTION. 
71 
10. 
Lh “ on.” 
Kf “ off.” 
Eh “ off.” 
Lf “ on.” 
11. 
Eh “ on.” 
Lf “ on.” 
Lh “on.” 
Kf“off. 
12. 
Eh “ on.” 
Lf “ on.” 
Lh “ off.” 
Ef “off.” 72 
MATERIALS FOR A MEMOIR ON 
An Analysis of the Movements of the Raccoon, the 
Baboon, and the Sloth. 
In addition to the general remarks on animal movement and 
the analysis of separate phases of the limb positions, it has been 
thought advisable to describe a few forms in detail. 
With this object in view, figures of the raccoon (series 744), 
the baboon (series 747), and the sloth (series 750) are herewith 
presented. 
The Raccoon. (Series 744.) 
The raccoon (Procyon) has been accepted as a form worthy of 
careful analysis, since the genus is one of the most ancient of the 
extant Carnivora, and presents in its gait opportunity for ascertain- 
ing the manner in which a primitive flesh-eater moved when of 
small size and of short limb. (See p. 38.) 
The gait from Fig. Ito Fig. 4is in diagonal heterochiry. In 
Fig. 1 the right fore foot lingers so long on the ground that the 
left hind foot is about to come “ on” also. The right hind foot is 
about leaving, and the fifth toe projects backward. (See p. 51.) 
(Fig. 2 of series.) 
In Fig. 2 the right fore foot remains on the ground, the left hind 
foot now reaches the ground at its side, and the right hind foot is 
“ off.” The position is retained in Figs. 3, 4, and 5. 
In Figs. 5, 6, 7 the gait is left lateral heterochiry, the support 
being on the left legs, the fore limb being in forward movement 
and the hind limb being in backward movement. Fig. Bis a 
transitional form (the animal movement only resting on three 
legs) back to the diagonal heterochiry, as seen in Fig. 9, which 
retains the combination in one picture only, to be again in right ANIMAL LOCOMOTION. 
73 
lateral heterochiry in Figs. 10, 11, 12. The fifth toe of the right 
hind foot is here seen to extend horizontally. The change to 
(Fig. 3 or series.) 
(Fig. 4 or series. See p. 50.) 
(FIG. 12 OE SERIES.) 
diagonal heterochiry is made in Figs. 13,14 (which are repetitions 
of Figs. 1, 2, 3), and a stride is completed. The animal now 
alters its gait from heterochiry to synchiry. Fig. 15 is the form 
of transition. In Fig. 16 the change has been completed and the 
animal is sustained alone by both hind feet. He maintains this 
position in Fig. 17, but again is in a transition form of three legs 
on the ground in Fig. 18. 74 
MATERIALS FOR A MEMOIR ON 
In Fig. 19 the animal is in diagonal heterochiry, in which 
position the right hind leg shows the fifth toe in the axis of the 
leg, and greatly abducted from the fourth. 
(Fig. 19 of series.) 
In Fig. 20 it is again synchiral, the fore pair now assuming 
the work of supporting the body. The fore limbs are nearly at 
the extremes of forward and backward movement. 
The sole of the foot in the left fore foot is in part in aid of 
the limb, and presents an example of the plantigrade foot be- 
coming semi-digitigrade as the foot passes backward of the vertical 
line. 
(Fig. 20 OF SERIES.) 
It will be seen that the gait is irregular; it is first a walk or 
trot, afterwards assumes the position of pacing, and finally ends in 
a gallop, or as much of the latter gait as can be assumed to exist 
in an animal with short legs. 
The Baboon. (Series 747.) 
In the series of the baboon the animal is seen in the walk. 
The form was accepted for comparison with the raccoon because 
of the position of the animal near the other end of the scale of 
quadrupeds. The limbs have great length, and the intervals be- ANIMAL LOCOMOTION. 
75 
tween the two feet of a single pair when in extremes of forward 
and backward movement are correspondingly great. 
In Fig. 1 the animal has just left lateral support, in which 
both limbs move in the centre of the body by the left fore foot 
leaving the ground. In Fig. 2 the support is diagonal, and both 
limbs (right fore and left hind) are removed from the centre. 
This is retained through Figs. 3 and 4. In Fig. 5 the same dis- 
(Fig. 5 of semes.) 
position continues, but it is noteworthy because of the shape of 
the left hind limb, which resembles the shape of the ungulate 
foot. The right fore limb is now in the extreme of backward 
movement. 
(Fig. 6 of semes.) 
In Figs. 6 and 7 the position is left fore and right hind (lateral 
heterochiry). 76 
MATERIALS FOR A MEMOIR OX 
In Fig. 8 the laterals have changed to diagonals by the right 
fore foot coming down as the left leaves the ground. 
(Fig. 7 or series.) 
In Figs. 9, 10, and 11 the same position is maintained. The 
shape of the right fore leg as it nears the vertical position is note- 
worthy. 
(Fig. 8 or series.) 
The left hind foot has overtaken the lingering right fore foot, 
and three feet are on the ground. This position is instantly lost 
by the lifting of the left hind foot from the ground, when a diag- 
onal support ensues, which closely resembles in general effect the 
lateral support in Fig. 6. ANIMAL LOCOMOTION. 
77 
(Fig. 11 of series.) 
(Fig. 12 or series.) 
(Fig. 13 op series.) 78 
MATERIALS FOR A MEMOIR OX 
This position is maintained in Fig. 14. Fig. 14 is a repetition 
of Fig. 1, and the stride is complete. The gait is shifted to left 
laterals in Figs. 15 and 16, 
(Fig. 14 of series.) 
Figs. 13 and 14 can be compared with advantage with Figs. 3 
and 4,13 and 14 of Procyon (series 744). The feet are relatively 
in the same position. 
In the baboon the dorsal line changes scarcely at all from that 
in the other figures. In Procyon the dorsal line is more convex 
in these figures than in any others. 
The most characteristic position of Procyon is the laterals in 
Figs. 11 and 12. The limbs are in the extreme of movement, 
the hind backward and the fore forward. The most character- 
istic position of the baboon (Fig. 6) is the reverse of this, the hind 
limb being forward and the fore backward. The relative places 
of the “on” and “off” feet are directly opposed. 
The Sloth. (Series 750.) 
The sloth does not use the limbs in lateral heterochiry. He is 
compelled to keep the feet “on” in combinations which will insure 
his support. Owing to the hook-like grasp of the feet, the hind 
limb becomes markedly rotated outward as it passes back of the 
vertical line (see p. 38). 
Fig. 1 is in the same position as in the baboon (Figs. 6 and 7), 
—i.e., the fore and hind limb of the same size (viz., the left) 
are at the nearest point possible one to the other. But the other 
two limbs, while lying at the farthest point possible from each ANIMAL LOCOMOTION. 
79 
(Fig. 1 os’ series.) 
(Fig. 2 of series.) 
(Fig. 3 of series.) 80 
MATERIALS FOR A MEMOIR ON 
other, are not “off,” as is the case with the baboon. Save in this 
instance, the positions are the same. 
The attitude remains unchanged in Fig. 2. In Fig. 3 the left 
fore limb has left the perch, and is projected directly upward. 
(Fig. 4 of series.) 
In Figs. 4 and 5 the left fore limb is swung forward above the 
level of the perch, and the right hind leg is “ off” and projects 
(Fig. 5 of series.) 
upward. In Fig. 6 all limbs are again “on,” as in Fig. 1, The 
left fore and the right hind limb have just come “on.” The 
position is maintained through Figs. 7, 8, and 9. ANIMAL LOCOMOTION. 
81 
(Fig. 6 op series.) 
(Fig. 7 of series.) 
(Fig. 8 of series.) 82 
MATERIALS FOR A MEMOIR ON 
Figs. 7 and 8 closely resemble each other. They differ in the 
degree of outward rotation of the left hind leg. It is wider in 
Fig. 8 than Fig. 7, and is rotated farther outward. The head in 
Fig. Bis nearer the beam than in Fig. 7. For consideration of 
the outward rotation, see p. 89. 
In the interval between Figs. 9 and 10 both the left hind and 
(Fig. 9 or series.) 
(Fig. 10 of series.) 
the right fore limb have left the perch and remain “off” through 
the remaining Figs. 11 and 12. 
In Figs. 10, 11, and 12 the manner in which the support is 
maintained while the two limbs are “off” is illustrated. It is 83 
ANIMAL LOCOMOTION. 
strictly diagonal heterochiry. Yet in Fig. 12 the same positions 
as in Figs. 1, 6, 7, 8, and 9 are about to be assumed, showing that, 
(Fig. 11 or series.) 
while support may be diagonal, the limbs which relatively are 
farthest apart or the nearest together are laterals. Thus the gait 
(Fig. 12 or series.) 
of the sloth is peculiar in having all four feet “ on” at one stage 
of movement, while the gait is the usual disposition of alternate 
feet by diagonal. 84 
MATERIALS FOR A MEMOIR OX 
ZOOLOGICAL CONSIDERATIONS. 
The object which the writer has had constantly in view in 
studying the photographs is to endeavor to determine the value 
of attitude and gait to classification. Many of the notes bear to 
a greater or less extent upon zoology, but a few which appear to 
apply in an especial way to taxonomy are conveniently brought 
together at this place. 
As is wrell known, the mauus and pes present a plan in the 
arrangement of the elements which may conveniently receive the 
name of the lateral and median series. In the manus, the cunei- 
form and the unciform bones constitute the lateral, and all the re- 
maining bones the median, series. In the pes, the calcaneum and 
cuboid bone are embraced in the lateral series, and all the remain- 
ing bones form the median. With this necessary understanding, 
the writer will now proceed to state the premise upon which he 
undertook a special examination of the manus and pes in connec- 
tion with the phenomena of limb-movement. The episode may 
be accepted as an instance in which the photographs suggest vari- 
ous lines of research, even though nothing of especial value be 
claimed for the results here secured. 
When it was determined, chiefly by the study of the stroke (see 
p. 50), that the foot comes down by the outer border and leaves 
by the inner, an attempt was made to ascertain by examination of 
the structure of the carpus and tarsus the mechanism which corre- 
lated with the movement. It wras expected that an oblique line 
by which the strain could be traced across the small bones would 
be found. The views of Leboucq,* which embrace a path of 
precisely this character in the embryonic form of the tarsus of 
mammals, appeared to be confirmatory of this expectation. 
The well-known fact that the calcaneum occasionally ossifies 
with the scaphoid bone in the human foot,f and is at times found 
united to it by synchondrosis,J was suggestive that the oblique 
axis could be determined in that form with whose structure anat- 
* Arch. Biol. (Brussels), iv. 35. 
f Gruber, Mem. cle I’Acad. de St. Petersbourg, ser. vii., p. 9, Taf. xvii 
Holl, Arch, fur Ivlin. Chirurg., 1880; Zuckerkandl, Wiener Med. Jahrbuch, 
1880. 
J Weber M., Yerslag. der kon. Ak. Amsterdam, 1883, xviii. 121 85 
ANIMAL LOCOMOTION. 
omists are most familiar. Aeby* describes a similar arrange- 
ment in the foot of the gorilla. 
It was reasonable to infer from these data that the disposition 
of the calcaneum to transfer the strain transmitted to it across the 
foot to the scaphoid would characterize the mammalian foot. 
A careful examination of the tarsus has not warranted the in- 
ference. As shown by Leboucq, the arrangement exists in the 
embryo, but it is not maintained as a rule in the adult, nor is it 
seen in the phylogeny of the group. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 2.—Diagram of the relation of the astragalus (A), the calcaneum (Cn), the scaphoid 
bone (S), and the cuboid bone (Ob) in the foot of mammals. 
Fig. 3.—Diagram to exhibit the disposition for the astragalus to form a junction with 
the cuboid bone. (Letters as in Fig. 2.) 
Fig. 4.—Diagram to exhibit a disposition for the calcaneum to form a junction with 
the scaphoid bone. (Letters as in Fig. 2.) 
The statement of Kowalevnsky is accepted, that the earlier 
forms of mammals exhibit lines of support which correspond to 
the arrangement of the bones of the leg. (See Fig. 2.) But in the 
animals now living, the lines of the bones of the carpus and tarsus 
do not as a rule show such independence. The bones of the tar- 
sus are almost invariably more or less displaced. In the tapir 
and the rhinoceros, which are the best living examples of related 
forms to the earlier forms, the acquired support from adjusting 
rows is as exact as in any of the numerous recent specialized 
forms which at present inhabit the earth. 
So far as examined, the calcaneum articulates with the scaphoid 
bone in the following genera only : 
Homo, 
Troglodytes, 
Equus (variable; sometimes 
astragalo-cuboid), 
Dipus, 
Coelogenys, 
Erethizon (variable). 
* Morph. Jahrbuch, iv., 1878. 86 
MATERIALS FOR A MEMOIR ON 
Herewith are given examples of the common cuboido-astraga- 
loid articulation : 
Hyrax (not marked), 
Rhinoceros, 
Amynodon, 
Ungulata, 
Procyon, 
Ursus, 
Erignatbus, 
Menodus, 
Palseosyops, 
Creodonta, 
Macropus, 
Phascalarctos, 
Dicotyles, 
Hippopotamus, 
Erethizon (variable), 
Arctomys, 
Myrmecophaga, 
Elephas, 
Equus (variable; sometimes 
calcaneo-scaphoid). 
Neither the calcaneo-scaphoid nor cuboido-astragaloid articula- 
tion is found in the following : 
Dasyprocta, 
Capromys, 
Fiber, 
Hystrix, 
Hyena crocuta, 
Orycteropus(variable; tends 
to calcaneo-scaphoid), 
Homo (variable; sometimes 
calcaneo-scaphoid). 
While a fixed arrangement of the parts in an assumed oblique 
axis is thus undetected, the examination was fruitful of one result, 
—namely, that when in addition to the axial disposition of the 
tarsal bones one to another and the lateral adaptation of parts in 
transverse rows was departed from, the departure took place in 
one of two ways,—either by the calcaneum reaching the scaphoid 
(i.e., by a direction downward and inward) or by the cuboid bone 
reaching the astragalus [i.e., by a direction upward and inward). 
It is thus demonstrable that the elements in the tarsus which first 
distribute the weight of the outer border of the foot as it comes 
to the ground transmit the impact inward in an oblique manner, 
and, it may be assumed, tend to throw the weight of the limb 
towards its axial line, which sustains the weight of the body 
when the limb is in the vertical position. 
In the study of the phylogeny it will be seen that the more 
distal of the two bones is first pressed inward, and that this 
arrangement obtained not only in the first (with the exception of 
Coryphodon), but in most of the extant forms. Why it should 
ever have departed from this arrangement and reversed the in- 
ward impact to the calcaneum is not an easy question to answer. ANIMAL LOCOMOTION. 
87 
It is worthy of remark that in Equus and Dipus we have highly 
specialized forms of foot-structures; and in Primates, while the 
foot on the whole is generalized, the astragalus sends a remark- 
ably inward directed and obliquely placed neck in a direction 
which would render it difficult for the cuboid bone to reach it. 
It must be acknowledged as a great difficulty how an inter- 
mediate group arose in which a simple form of tarsal dis])osition 
is retained. While from facts presented by Professor Flower it 
would be natural to assume that Orycteropus might move the 
foot in a manner different from Myrmecophaga, nothing can be 
urged why Hyena should differ from Canis, or Dasyprocta and 
Capromys from Arctomys. 
An examination of the carpus showed less disposition for the 
outer elements of the series to be placed inward than is the case 
in the tarsus. The cuneiform bone, which corresponds in position 
to the calcaneum, and the unciform, which corresponds to the 
cuboid bone, remain in all forms of the manus in constant relation 
to the rest of the carpus. But the entire lateral division of the 
carpus exerts a disposition to displace the os magnus inward and 
upward in a manner which is strikingly exhibited in the follow- 
ing scheme. 
The os magnum articulates with the scaphoid bone in 
Coelogenys, 
Rhinoceros, 
Dicotyles, 
Hippopotamus, 
Tapirus, 
Sus, 
Chrysochloris. 
That is to say, the os magnum, in addition to articulating with 
its own axially disposed element, the lunare, secures an articula- 
tion with the scaphoid bone. 
The os magnum articulates with the lunare only in 
Dasyprocta, 
Capromys, 
Erethizon, 
Hyrax, 
Hystrix, 
Arctomys, 
Uintatherium, 
Elephas (variable with 
trapezoidal-luuare), 
Tapirus, 
Manatus, 
Orycteropus, 
Myrmecophaga, 
Myogale. 
In summarizing these results, it may be said that the fact of the 
outer border of the pes coming to the ground in the first stage of 88 
MATERIALS FOR A MEMOIR ON 
the stroke is in correlation with a disposition for one or more of 
the tarsal elements of the outer series to secure junctures—i.e., 
junctures not accounted for in the plan of the parts—with one or 
more elements of the median series. Relatively few genera resist 
this disposition. 
In the manus, the lateral series remains intact, but in a few ex- 
tant genera and in some extinct genera the outermost of the median 
series is seen to articulate with a carpal element which lies to its 
inner side. 
Deviations of the Trunk with Respect to a Hypothetical Longitudi- 
nal Axis. ■ 
An interesting series of comparisons can be instituted between 
the anterior and the posterior parts of the trunk in the various 
positions of the limbs. In illustration of this subject attention is 
directed to the deviations of the trunk in advance of the rump 
with respect to a line drawn horizontally forward from the base 
of the tail. Assuming that the beginning of such a line corre- 
sponds to the part which shows the least motion and passes to 
that which shows the most, it will follow that the fore part of the 
trunk, together with the whole of the regions of the head and the 
neck, will shift positions with respect to this line. In series 675 
the figures of the hog demonstrate that the body in advance of 
the rump are highest when the animal is resting on both hind 
feet. It is next highest when the animal has come down one 
fore foot. In the deer, when propped on the fore limbs, the animal 
sinks so low anteriorly as to permit the horizontal line to intersect 
the muzzle. The fact that the baboon exhibits no contrast of 
the kind named would lead to the conclusion that the clavicle 
prevents the fore part of the trunk from sinking,—a conclusion 
which is invalidated by the fact that the elephant shows a similar 
exemption. 
Relation between the Oblique Movement across the Foot and the 
Number of Toes. 
From the fact that the outer border of the foot first strikes the 
ground and that the inner border last leaves it, one can create a 
proposition to which the following facts are corollary. (See pp. 
42, 50.) ANIMAL LOCOMOTION. 
89 
When the outer border is longer and stouter than the inner, 
the first-named parts of support are of more importance than the 
last. The difference in this regard between the foot of man and 
that of the bear should be the difference between the respective 
lengths of the first and the fifth toes. 
When the inner toe is rudimental, or lost, the foot has left the 
ground before the inner border is reached. But it is not so evident 
why the fifth toe should be lost. One wrould suppose that this toe 
would be the most persistent. The sequence of the limbs of the 
horse from the five- to the single-toed forms would be of interest 
to study in this connection. 
Rotation of the Limb. 
In another relation than that included in the foregoing the 
study of the photographs has been of interest. Allusion is partic- 
ularly made to the forward swing of the fore limb and the outward 
rotation of both limbs (for inward rotation see p. 59). 
The extent of the forward swing is found to correspond to the 
extent of the trochlear surface of the humerus as it enters into 
the composition of the elbow-joint. In addition to this fact atten- 
tion may be called to the difference in the length of the olecranon 
in different animals. The olecranon is greatly longer relatively 
to the shaft of the ulna in primitive types of Mammalia than in 
the more specialized, as the writer has been informed by Professor 
W. B. Scott. The same difference is found to obtain between 
Dicotyles and Sus. May it not be claimed that the difference 
correlates with the facilities possessed of maintaining the fore limb 
in backward strain ? The enormous leverage secured by a long 
olecranon must enable the limb to maintain a strong position for 
the limb when it is held in backward strain as compared to one 
in which the olecranon is short. This must be especially marked 
when the humerus is long, as is always the case in these types. 
The mechanism which accompanies the rotation of the limb 
outward at the knee after it has passed the vertical line is as- 
sociated, as has been seen, with inward rotation of the hock. 
This form of torsion is described (see p. 45), and the springing 
power of the limb is a resultant. The amount of springing power 
should correlate with the torsion, and the facets by which twists 
are effected be indices of the act. The conversion of the calcaneo- 90 
MATERIALS FOR A MEMOIR ON 
cuboidal articulation into a convexo-concave joint, in forms in 
which the oblique impact is cuboido-astragaloid, would look as 
though such impact favored torsion. 
The study of the rotation of the limb is conveniently under- 
taken in the elephant, since the fur is here absent. A number 
of the positions assumed by the limbs is illustrated in series 
733, Figs. 1 to 12. (See the figures of the fore limb of the 
elephant.) 
The width of the limb at the elbow is observed to be less in 
backward strain than in the recover. 
In Figs. 1, 2, 3, and 4 the olecranon is in line with the posterior 
border of the arm above the elbow. 
In Fig. 4 the foot is leaving by its inner border. In Fig. 5 
the olecranon is more in view, since it is turned out, at the same 
time the foot is now everted (i.e., rotation outward has taken place 
as the limb passes from impact of backward strain to that of re- 
cover). Extreme position of eversion (Fig. 8) is coincident 
with the distance between the olecranon and the humerus, and 
the greatest reduction of distance between humerus and anterior 
border of the arm. The posterior border of the arm is here 
beginning to leave the side of the trunk, and a white light is re- 
flected from over the triceps muscle. 
During the forward movements of Figs. 9 to 12 the limb is 
slowly passing back to the position where the olecranon is again 
in line with the posterior border of the limb (i.e., strictly speaking, 
in profile of the limb), and the foot is preparing for a second 
period of impact against the ground. 
The lighter shade of the prominence at the back of the elbow 
answers to the position of the olecranon; the elongated mass of 
light shade which extends parallel to the arm between the elbow 
and the shoulder answers to the position of the outer border of the 
humerus. It is evident by the pictures that the distance between 
the light over the humerus and over the olecranon is variable. 
But it is known that the actual distance is invariable, and there- 
fore the apparent variance is due to the motion of the limb in 
rotation at the shoulder, by which the region of the back of the 
elbow is moved somewhat outward. At the same time the dis- 
tance from the outer border of the humerus and the anterior 
contour is lessened as rotation takes place. These facts being Series 733, Figs. Ito 12, illustrating the rotation of the fore limb of the elephant (luring the act of recover. To be studied from to left, beginning at the top row. ANIMAL LOCOMOTION. 
91 
borne in mind the following additional observations can be 
made: 
The torsion of the limb is pronounced in the Tylopoda ex- 
amined,—viz., the camel, the dromedary, and the guanaco. This 
fact should not be disassociated with the absence of anchylosis be- 
tween the cuboid bone and scaphoid bone with these animals. 
In contrasting the above examples with the Pecora,—e.g., the 
other ruminants, excepting the family of the musk-deers, not 
examined,—the following structural features may be mentioned 
as correlations of peculiarities of gait. 
In the Tylopoda, when the limb is supporting the body, the 
hoof is always in line of support with the rest of the limb. In 
the deer the hoof and digits are angulated with the rest of the limb. 
In the Tylopoda the joints are thick, and the outlines are dis- 
tinctly seen. The fore limb of the Tylopoda is never noticed at 
a point posterior to the withers, but leaves the ground at an angle 
of about minus forty degrees. The fore limb of the Pecora is 
vertical at a point at the centre of the trunk, and leaves the 
ground at about minus fifteen to twenty degrees. When the limb 
is off the ground, the digits are flexed to a greater degree in the 
Tylopoda than in the Pecora. 
In the Pecora the limb is smaller and more delicate in propor- 
tion to the bulk of the body; the spread of the hoof is less, and 
the movement of the bones each in the other more precise than 
in the Tylopoda. 
The vertical position of the fore limb under the centre of the 
trunk is possible, because of the oblique position of the humerus. 
The heavily-built bovine animals present the same contrasts as 
the deer, with the exception that the fore limb is carried less back- 
ward. (See j). 45.) 
The camel has a relatively short metapodiura. The joints 
present curved contours in place of angular ones,—excepting the 
angle formed by the hock,—and even this is less pronounced than 
in other ruminants. 
While the general features of the quadrupedal motion are in all 
animals the same, minor peculiarities of the carriage have doubt- 
less taxonomic significance. A number of these will be indicated. 
Minor Peculiarities. 92 
MATERIALS FOR A MEMOIR ON 
The dog when off the ground flexes the fore legs, the cat ex- 
tends them. This probably correlates with the size of the supra- 
spinous fossse of the scapulae in the two animals, (See p. 84.) 
The extended fore leg in the cat is parallel to the long axis of 
the trunk, while in all the ungulates it forms an angle to this axis. 
The angulation of the parts in ungulates is subject to variation, 
being more open in the deer tribe than in the ox; in a word, in the 
lighter-bodied as contrasted with the heavy-bodied forms. The 
humerus in backward movement is nearly horizontal in the Pecora. 
(See pp. 42, 45.) 
The enormous size of the anterior dorsal spines in the hoofed 
animals, their smaller size in the claw-footed, their entire absence 
in Dipus and the bat (in which animals the fore legs are not used 
for support), the trend of the great extrinsic muscles of the fore 
limb towards the head, all prepare the observer for some tax- 
onomic values in the relations existing between the strength of 
the cephalo-humeral muscles, the obliquity of the fore leg in 
forward movement, and the size of the anterior dorsal spines, 
and possibly in the shapes of the atlas and axis. 
The camel protrudes and withdraws the under lip each time 
the fore and hind limbs are shifted. 
In the North American buffalo the prepuce is drawn backward 
when the hind limbs are in backward strain. 
Characters pertaining to the Superficies emphasized in the Pho- 
tographs. 
It is a well-known circumstance that the photograph will bring 
out details of structure which are not seen by the unaided eye. 
Thus, an inscription on a tombstone which was covered by lichen 
and was quite illegible was found by Professor J. T. Rothrock to 
be read with the greatest ease when seen photographed after the 
ordinary manner. The photographs of the series of animals 
studied reveal similar interesting features. The spots on the lion 
and the lioness are much more distinct than they are in the living 
models. In the lioness, in addition, five minute points are detected 
on the back of the trunk. They probably correspond to the em- 
inences of the skin over the spines of the dorsal vertebra. 
A fairly recognizable description could be drawn up of the 
superficial muscles of the limbs, especially of those fleshy masses ANIMAL LOCOMOTION. 
93 
which pass from the trunk to the limbs. The reflections of light 
from the hair of the figures of the horse may be ascribed to the 
changes in degrees of convexity or concavity of the superficial 
muscle-masses, while some of the stripes of the tiger, especially 
those of the fore limb and the neck, will be found to answer 
to the depressions existing between well-defined positions of 
muscles which can be named with accuracy. In the figures of the 
roan horse (series 582) the black patch on the rump corresponds 
to the great biceps muscle. 
In the horse (series 579) the depressions between the muscles 
of the posterior aspect of the thigh are most marked when the 
limb is in the first stage of the recover, but are obliterated when 
the limb is in backward strain. The masses at the inner border of 
the thigh, as seen in the horse (series 582), are nearly flat when 
the limb is off the ground, but conspicuously convex when the 
animal is using the limb for support. 
In the dog, when both fore feet are*off the ground, the muscles 
which pass from the trunk to the fore limbs are exceedingly 
tense. 
On the Significance of the Skin-Folds on the Trunk of the Hog. 
A number of minute changes in the contour of the animals are 
worth noting. In the figures of the hog (series 673 to 675), at the 
time when the limbs of a single side are the nearest one to the 
other the skin is observed to be thrown into a series of vertical 
folds. It is suggestive of the mechanical origin of the bands in 
the armadillo that the lines in the hog are in the same position 
as the bands. They appear to differ only in the circumstance 
that the folds are transient, while the bands are permanent. (See 
p. 45.) 
The Mane. 
Each time the horse, in the series 590, leaves the ground by one 
of the hind feet the mane streams backward. In series 638, as 
the animal descends the mane streams upward. This change in 
position is caused by the motions of the head and neck upward 
and downward. (See especially figures of the horse rocking, series 
649 A. Seep. 48.) 94 
MATERIALS FOR A MEMOIR ON 
The Significance of the Keel on the Metapodium. 
The presence of a ridge on the distal ends of the bones of the 
tarsus and carpus, as well as on the first and second rows of pha- 
langes, is indicative of a precision of motion in the joints of 
which it constitutes a part. Such ridges are known as keels, and 
are found in the feet of the ruminants, excepting the group of the 
camels, and in the horse. The primitive types of mammalian life, 
as has been pointed out by Professor E. D. Cope,* were without 
the keel. It first appeared on the posterior surface of the articu- 
lar surface, and subsequently upon its anterior surface as well. 
These facts suggest the conclusion that the ridge was developed 
for some exigencies of the foot while in backward strain, and in 
the action of the transition from “on” to “off,” since the keel 
first appears on the flexor side of the foot, and that, since in 
extant animals the camel and its kin are without the keel, a 
careful comparison of the motions in these creatures with those of 
the other ruminants would be suggestive of the use of the keel, 
and lead to some interesting differences between the gaits of 
primitive and specialized types. 
After having made careful studies of the series of the Egyptian 
camel (736), the Bactrian camel (737 to 742), and the guanaco 
(743), I have been unable to find any features which correlate 
with these anatomical peculiarities. 
Evolution of the Gait. 
The gait in its various expressions is based upon the correla- 
tions between the fore and the hind limbs. Assuming that the 
simplest movement is an alternate action of a single pair (syn- 
chiry), the simplest gait is that in which this alternation occurs 
in each pair independently. The gallop is thus the simplest gait, 
since the fore pair and the hind pair are independent. But the 
gallop depends upon a high momentum, and we must assume 
that the primitive animals were slow walkers. When in a slow 
rate the same independence is observed,—i.e., when the right fore 
foot is moved forward at the same time as the right hind foot 
(lateral heterochiry),—the two pair act rhythmically, and the feet 
“ keep step.” This is seen in the rack, which thus becomes a 
* The Origin of the Fittest. ANIMAL LOCOMOTION. 
95 
practicable gait for a primitive creature. The only objection to 
this conclusion is the fact that in the giraffe, which is a specialized 
and aberrant form,—and the legs are remarkable for their length, 
—we have the best example of a natural pace. 
The simplest forms of moving appendages are seen in the 
Nerita, one of the fresh-water worms, in which the bristle-like 
rods are moved in all directions without concert. In other forms, 
as in the sea-hare (Aphrodite), the bristles move in numerous 
lines extending alongside of the body, but each line in turn being 
independent of those adjacent to it. The next arrangement ob- 
tains in myriapods, whose feet, while in pairs, are seen to move 
as the horse’s in pacing,—i.e., each row acting as a whole, and the 
two rows alternating. In the lower crustaceans the same method 
obtains. In the higher crustaceans, as in the crab, the two parts 
of a single pair may act together. 
It stands to reason that when to one side of the body a re- 
inforcement is received from a limb of the opposed side and of a 
different pair advancing to the median line, a relatively high 
degree of development has been attained. In a phrase, in animals 
with highly developed central nervous systems the bilateral co- 
ordinations become as practicable as the unilateral. 
The question of the manner of using the feet in progression is 
also likely to be a subordinate one to the question of the size and 
the bulk of the body. In short-legged, heavy animals of slow 
movement, the support of the centre of the heavy trunk by the 
diagonal use of a fore and a hind limb was probably early obtained. 
Nevertheless the Echidna, a good example of an animal possessing 
a large, heavy body and short limbs, walked by diagonal hetero- 
chiry.* The feet, however, did not approach each other towards 
the centre of the trunk, as is the case in the walk and the trot of 
the horse, but kept to the side of the body. 
In long, slender natatorial forms, which would occasionally 
slide among the ooze of a river-bed,—such an animal, for exam- 
ple, as the Potomogale,—doubtless specialization can be attained 
in the line of development of many of the gaits.f We have 
| The crocodile of the Jumna, according to Hornaday (“Three Years in 
the Jangle,” 1885, p. 55), can stand upon the legs in the same manner as a, 
terrestrial quadruped. 
* This was observed in the specimen at the Zoological Garden, Philadelphia., 96 
MATERIALS FOR A MEMOIR ON 
seen that the giraffe uses the pace for all rates of movement; also 
that the horse modifies his paces by the character of the ground 
he traverses. It is probable in like manner that an animal will 
by natural selection determine his methods of progression. Marsh- 
dwellers are uniformly of the heavy-bodied, short-legged type. 
In an animal emerging from the marsh to the plains the limbs 
would become more compact and longer and the gait more various.* 
Catonf states that the Virginia deer bounds up once or twice at 
the beginning of his gait, to observe the surrounding country be- 
fore he settles down to a steady run. This habit would be of no 
use in an animal living on a prairie, and is absent in the mule- 
deer. Mere speed is not a necessity of a change of gait, A trot 
can be based on the walk; the fast pace on the slow pace. In the 
opinion of Dr. M. H. Cryer, a horse in going over a hurdle em- 
ploys the same division of his stride as in the run. 
Variability of gait in a single animal may be accepted as an 
evidence of high development. Diversity of function in the 
study of the gait is of the same value as in other subjects of 
biology. Thus, an animal starting a movement on the laterals 
by bringing into use a member of the opposite side, so that three 
feet may be on the ground at the same time, can develop a walk 
from the primitive pace, and can either maintain it at will or, 
shifting from the right to the left lateral support, show a high 
degree of division of functional labor in the use of the limb. In 
like manner, when an animal wishing to increase his rate of speed 
can by election leave the walk to amble, gallop, trot, or pace, an 
advantage is secured over another animal in which the choice is 
either withheld or limited. 
Of the two pairs of limbs, the front one is the more adaptive 
for the reason that it is capable of so many secondary modifica- 
tions, as grasping, flying, etc. We may assume by analogy that 
the fore limbs are active in changing gaits, the hind limbs acting 
in a more rigid and uncompromising manner. (See p. 51.) 
* According to F. 0. Selous, Proc. Zool. Soc. London, 1881, p. 726, Rhi- 
noceros simus can gallop. 
| Antelope and Deer of North America, p. 270. 97 
ANIMAL LOCOMOTION. 
THE MOVEMENTS OF THE HUMAN SUBJECT. 
The motions of the hands and feet are essentially those of the 
quadruped. In the series 258, the man rising from a recumbent 
position on the ground first uses the left arm for support, subse- 
quently transfers the weight to the right, and after gaining the up- 
right position retains the hand last named as though it were in 
the first stage of the recover, as seen in the foot of the quadruped. 
The dictum made in connection with the flexor muscles aiding the 
foot of the quadruped to maintain itself on the ground is here ex- 
emplified (p. 42). It is interesting to note that the moment the 
hand leaves the ground it becomes markedly flexed. 
Gait. 
In series 69 the position of the arms (being thrown back at the 
time that the hind leg of the opposed side is also thrown back) 
sustains the assertion that the motion of the limbs of man is heter- 
ochiral. The chief distinction between the gait of man and that of 
the quadruped is the degree of torsion of the vertebral column. 
For a good illustration of this torsion the figure of the boxer 
(series 333) may be consulted. 
The Action of the Disengaged Limb 
In series 311 and 312, while the right hand is engaged in 
throwing a weight the left is in a state of great tension. The 
limb is extended and the fingers are abducted. The fingers remain 
extended save at the terminal phalanges, and show activity of the 
interossei muscles. The position just named is suggestive and 
presents a raison d’etre for the following reflections : 
First, that the unemployed arm is thrown into a state of ex- 
citement because of the intentive strain on groups of muscles in 
close co-ordination with them,—viz., the muscles of the limb of 
the opposed side. The limb cannot repeat the exact attitude of the 
one in use, and naturally tends to take on the form of the primal 
limb. This form is that of a motion as though it were on the 
ground and serving the purposes of progression. As is known 
from the study of the quadruped, the limb after extension passes 
gradually into flexion. It is evident that the interossei muscles 
would not flex the terminal phalanges if the foot were on the 98 
MATERIALS FOR A MEMOIR ON 
ground, but would simply hold the ends of the toes firmly to the 
plane on which the animal is moving. The toes are also markedly 
abducted in the same position. The attitude taken by the human 
fore limb is precisely that of the fore limb of the quadruped en- 
gaged in terrestrial progression, and is modified in its action solely 
by the circumstance that it “claws the air.” The function of the 
interossei would appear to be the retention of the phalanges of the 
terminal row against the ground as the last act of the behavior of 
the foot in the first stage of the recover. 
Second, that the occurrence of convulsive seizures, in which the 
limb assumes the position just described, may not necessarily be 
the result of an irritation of the centres which control the co-or- 
dination, but an evidence of a profound irritation elsewhere in the 
economy. This phenomenon properly belongs to the group of 
influences described by Drs. Mitchell and Lewis.* 
To a still greater extent than in the quadruped the superficial 
muscles are conspicuous. It is of interest to note that the sartorius 
muscle may be tense even when the foot is on the ground, as is 
observed in the figure of a man lifting a weight (series 322, Fig. 
12). In various attitudes the several portions of the trapezius 
muscle are contracted. In series 323, Fig. 9, in the figure of 
a man engaged in lifting a dumb-bell, the upper portion of the 
dorsal division of the muscle is enormously enlarged. 
Oscillation. 
The single series designed to illustrate the movements of the 
pelvis in walking is not in all respects satisfactory. 
Since the index at first inclines to the right side, which corre- 
sponds to the limb which is off the ground, the idea is at once 
suggested that the inclination is greatest towards the side not bear- 
ing weight, especially when it is noted that the index is vertical 
and parallel to the vertebral column when the legs are both on 
the ground. But when the left foot is lifted the lever remains in 
the vertical position, and no definite conclusion as to the effect 
of the movements of the limbs on the oscillation of the level is 
determined. 
* Philadelphia Medical News, 1885, vol. xlviii. p. 169. 99 
ANIMAL/ LOCOMOTION. 
FLIGHT. 
The flight of the bird is illustrated in series 755, 756, 757, 
pigeon; 758 to 762, cockatoo; 763, 764, hawk; 769, 770, eagle. 
The following conclusions have been drawn from the photo- 
graphs : 
The wing is extended upward from the horizontal position by 
the deltoid and latissimus dorsi muscles to a line which is perpen- 
dicular to the body, and is quickly again depressed to the hori- 
zontal position by the pectorals. (See p. 40.) This constitutes 
the first stage of the “ stroke.” 
“ Recover” is initiated by an inward rotation of the humerus, 
semiflexion of the wing at the elbow (the pinion remaining ex- 
tended and directed obliquely downward and outward), and is car- 
ried well forward to a degree sufficient, when seen in profile, to 
conceal the head. In this position the primaries are semi-rotated 
so as to present the least amount of surface to the air in the direc- 
tion in which the bird is moving. The impetus excited by the 
“stroke” carries the bird upward and forward. In the second 
stage of “recover” the humerus is rotated outward, the arm is 
quickly raised, the primaries restored to the position seen in the 
bird at rest, and the wing is a second time ready for the “ stroke.” 
(See p. 38.) 
In the eagle and the hawk the legs are in the position of the 
“stroke” when the wings are similarly placed. During the 
“stroke” the legs move backward. This position continues 
during the “ recover” of the wing, so that the time of the “ re- 
cover” is also that of the “ recover” of the leg. 
Biological Department 
University oe Pennsylvania, 
July 1, 1887. 100 
MATERIALS FOR A MEMOIR ON 
APPKNDIX. 
A LIST OF THE QUADRUPEDS AND BIRDS REPRESENTED IN 
THE PHOTOGRAPHS. 
EDWIN A. KELLEY. 
Series 563-657. Horse—Equus caballus, Linn. 
“ 658-664. Mule, hybrid—c? E. asinus and E. caballus. 
“ 665-668. Ass—Equus asinus, Linn. 
“ 669-672. Ox—Bos taurus, Linn, 
“ 673-675. Sow—Sus scrofa, Linn. 
“ 676-679. Goat—Capra bircus, Linn. 
“ 680. Oryx—Oryx leucoryx, Pall. 
“ 681, Virginia Deer—Cariacus virginianus, Gm. 
“ 682. Fallow Deer—Dama vulgaris, Gray. 
“ 683. Virginia Deer—Cariacus virginianus, Gm. 
“ 684-691. Fallow Deer—Dama vulgaris, Gray. 
“ 692-695. Elk—Oervus canadensis, Schreb. 
“ 696. Eland—Oreas canna, H. Smith. 
“ 697-698. Dorcas Gazelle—Gazella dorcas, Linn. 
“ 699-700. American Bison—Bison americanus, Gm. 
“ 701-702. White-tailed Gnu—Connochsetes gnu, Zimm. 
“ 703-715. Dog—Canis familiaris, Linn. 
“ 716-720. Cat—Felis domestica, Bris. 
“ 721-726. Lion cT—Felis leo, Linn. 
“ 727-728. Lion “ “ “ 
“ 729-730. Tiger —Felis tigris, Linn. 
“ 731. Jaguar—Felis onca, Linn, 
“ 732-735. Elephant—Elephas indicus, Cuv. 
“ 736. Dromedary—Camelus dromedarius, Linn. 
737-742. Bactrian Camel—Camelus bactrianus, Linn. 
“ 743. Guanaco—Lama huanacos, Mol. 101 
ANIMAL LOCOMOTION. 
Series 744-745. Raccoon—Procyon lotor, Linn. 
“ 746. Capybara—Hydrochcerus capybara, Erxl. 
“ 747-749. Chacma Baboon—Cynocepbalus porcarius, Bodd. 
“ 750. Sloth—Cholcepus hoflfmani, Peters. 
“ 751-754. Kangaroo—Macropus giganteus, Shaw. 
“ 755-757. Common Pigeon—Columba livia, Bris., var. domestica. 
“ 758-762. Cockatoo—Cacatua galerita, Lath. 
“ 763. Red-tailed Hawk—Buteo borealis, Gm. 
“ 764. Fish-Hawk—Pandion haliaetus, Linn, var. carolinensis, Gm. 
“ 765-768. Turkey-Vulture—Cathartes aura, Linn. 
“ 769-771. American Eagle—Haliaetus leucocephalus, Linn. 
“ 772-778. Ostrich—Struthio camelus, Linn. 
“ 774-775. Adjutant—Leptoptilus argala, Lath. 
“ 776-780. Groups of birds, as follows: 
Muscovy Duck—Cairina moschata, Linn. 
Canada Goose—Branta canadensis, Linn. 
Blue Goose—Anser ccerulescens, Linn. 
Bar-headed Goose—Anser indicus, Lath. 
Chinese Goose—-Anser cygnoides, Linn. 
European (Mute) Swan—Cygnus olor, Gm. 
American Swan—Cygnus americanus, Sharpl. 
Black Swan—Cygnus atratus, Lath. 
Sand-hill Crane—Grus canadensis, Linn. 
Australian Crane—Grus australasiana, Gould. 
Demoiselle Crane—Anthropoides virgo, Linn. 
Crowned Crane—Balearica pavonina, Linn. 
White Stork—Ciconia alba, Bechst. 
Black Stork—Ciconia nigra, Linn. 
Adjutant—Leptoptilus argala, Lath, 
etc. 
“ 781. Chicken—Gallus bankiva, Temm., var, domesticus. 
The following list embraces the series that are mentioned by number in 
the text of the report: 
258 576 612 633 675 695 729 747 760 
311 579 616 637 677 703 730 750 761 
312 581 617 641 680 704 733 755 762 
322 594 619 642 681 707 743 756 763 
323 595 622 649 a 682 709 744 757 764 
333 601 631 658 682 a 720 745 758 769 
574 602 632 670 683 728 746 769 770 INDEX. 
Action of limb in “ going off,” 49. 
Age, factor of disturbance, 67. 
Ape, 42. 
Aphrodite, 95. 
Armadillo, 45. 
Gait, contrasts of, 66. 
evolution of, 94. 
graphic method of study, 67. 
heterochiral, 63. 
human, 97. 
intervals in, 63. 
numerical method of study, 62. 
quadruped, 61. 
synchiral, 61. 
transitions in, 66. 
Gallop, 62. 
Giraffe, 45, 66. 
Goat, 48, 49. 
Guanaco, 94. 
Baboon, 42, 65, 74, 88. 
Backward strain, 44. 
Bat, 92. 
Bear, 89. 
Body, influence of, on foot, 48. 
Buffalo, Indian, 54. 
N. A., 64, 92. 
Camel, 47, 52, 92, 94. 
Capybara, 48, 51. 
Cat, domestic, 35, 54, 55, 64. 
Chimpanzee, 50. 
Crocodile, 95. 
Heel, depression of, 58. 
Hippopotamus, 61. 
Hog, 45, 55, 61, 88. 
Horse, 35, 45, 48, 49, 54, 55, 56, 58, 
63, 93, 96. 
Human subject, movements of, 97. 
Deer, Canadian, 88. 
fallow, 53, 62. 
mule, 60. 
Virginian, 35, 44, 45, 54, 88, 
96. 
Degrees, limb movements recorded 
in, 52. 
Dicotyles, 89. 
Dipus, 92. 
Dog, 43, 47, 52, 57, 58, 93. 
Inward rotation, 58. 
Kangaroo, 40. 
Keel on rnetapodium, 94. 
Kicking, act of, 58. 
Laterals in rack, 67. 
in walk, 67. 
Limb, action of, disengaged, 97. 
angulation of, at ankle, 55. 
oscillation of, 98. 
rotation of, 89. 
Limbs, action of, 40, 49. 
movement of, 39. 
position of, 40. 
position of, as to axis of trunk, 58. 
work done by, 40. 
Lion, 47, 52. 
Echidna, 54, 95. 
Effect of positions on head, neck, 
trunk, 47. 
Elephant, 35, 45, 47, 49, 52, 53, 58, 
90. 
Evolution of gait, 94. 
Extremity, anterior, 54. 
Eversion of foot, 50. 
Feet, position of, in “ recover,” 55. 
Flight, 99. 
Foot, eversion of, 50. 
striking ground on outer border, 
Mane, 93. 
Manner of limb going “off” in 
spring, 45. 
103 104 
INDEX 
Metapodium, keel on, 94. 
Minor peculiarities, 91. 
Motions same in all quadrupeds, 43. 
Movements, human subject, 97. 
limbs, 39. 
oblique, and numbers of toes, 89. 
Skunk, 35. 
Sloth, 35, 38, 42, 52, 78. 
Slowing up, 55. 
Solenodon, 55. 
Studio, plan of, at Univ. of Penn a. 
17. 
Superficies, characters of, 92. 
Sus, 89. 
Nerita, 95. 
Oryx, 62. 
Oscillation, 96. 
Ox, 35, 45, 54, 55, 64. 
Terms, use of, 36. 
Tiger, 47. 
Toes, length of, 48. 
obliquity of, 48. 
Torsion of trunk, 45, 57. 
Training, factor of disturbance, 57. 
Trot, 65. 
Turning round, 47. 
Turtle, 39. 
Tylopoda, 91. 
Pecora, 91. 
Potomogale, 95. 
Rabbit, 87. 
Raccoon, 35, 38, 43, 44, 47, 48, 64, 65, 
67, 72. 
Rack, 66. 
Reptile, 95. 
Rhinoceros, 96. 
Rotation, inward, 58. 
Walk, combinations in, 64. 
quadruped, 63. 
support of vertebral column in 
66. 
Salamander, 40. 
Serpent, 59. 
Skin-folds, 93. 
Wombat, 47. 
Zoological considerations, 84.