THE MECHANISM 
OF 
INDIRECT FRACTURES OF THE SKULL. 
CHARLES W. DULLES, M.D., 
FELLOW OF THE COLLEGE OF PHYSICIANS AND OF THE ACADEMY OF SURGERY OF PHILADELPHIA ; SURGEON 
TO THE OUT-PATIENT DEPARTMENT OF THE HOSPITAL OF THE UNIVERSITY OF PENNSYLVANIA 
AND OF THE PRESBYTERIAN HOSPITAL IN PHILADELPHIA. THE 
MECHANISM 
OF 
INDIRECT FRACTURES OF THE SKULL. 
BY 
CHARLES W. DULLES, M.D., 
FEy.OW OF THE COLLEGE OF PHYSICIANS AND OF THE ACADEMY OF SURGERY OF PHILADELPHIA J SURGEON 
TO THE OUT-PATIENT DEPARTMENT OF THE HOSPITAL OF THE UNIVERSITY OF PENNSYLVANIA 
AND OF THE PRESBYTERIAN HOSPITAL IN PHILADELPHIA. 
REPRINTED FROM THE 
TRANSACTIONS OF THE COLLEGE OF PHYSICIANS OF PHILADELPHIA, 
FEBRUARY 3, 1886. 
PHILADELPHIA: 
WM. J. DORNAN, PRINTER. 
1886. CONTENTS. 
PAGE 
Historical Study . 5 
Elastic Properties of the Skull 28 
Anatomical Peculiarities of the Skull .... 36 
Architectonic Peculiarities of the Skull .... 40 
Influence of Soft Parts and Contents of the Skull . 41 
Study of Cases 44 
Conclusion 50 
Bibliography 52 
Illustrations 57 THE MECHANISM 
OF 
INDIRECT FRACTURES OF THE SKULL. 
Historical Study. 
The earliest authentic mention of a fracture of the 
cranium occurring at another point than that upon 
which the violence which caused it was applied, is to 
he found in the writings of Hippocrates, who lived 
about 500 years before the Christian era. To call him 
a surgeon may seem startling to some who have thought 
of him only as the author of the oldest medical work 
now extant; but that he was a surgeon of great sense 
and acuteness his writings abundantly testify. Nor 
should it give offence to any that he should be claimed 
for the fellowship of surgeons, since, as Justamond has 
pointed out, in one of his admirable essays,1 the practice 
of surgery must have antedated that of physic ; for, as he 
remarks: " In the primary ages of mankind, when the 
most perfect of all created beings had yet scarce degen- 
erated from that state of perfection in which he was 
first produced from the hands of the Creator, disease 
1 Outlines of the History of Surgery. Surgical Tracts of the late J. 0. Justa- 
mond, F.R.S. etc. London, 1789. 6 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
was yet unknown upon the earth. Man had then no 
wants but such as the neighboring stream or the labor 
of his own hands would supply, no cares but those of a 
domestic nature, amply compensated by the satisfaction 
which attends them. His mind was not yet weakened 
by intemperance, nor his body impaired by debauchery; 
exercise was his only physic, and unbroken, undisturbed 
rest his only restorer. But, even in those happy and 
tranquil times, man was not exempt from the conse- 
quences of accidental violence. His body was not less 
exposed to common casualties and to a variety of strokes 
that might bruise or wound the flesh, or dislocate or 
fracture his bones. He might be torn by the fangs of 
some wild beast, or affected by the bite of some veno- 
mous insect. Such were the first and most natural evils 
to which man, in the place assigned him in the order of 
created being's, must have been obnoxious, and there- 
fore his thoughts would necessarily be engaged in 
finding out some means of relief for these accidents. 
Thus, from the nature of the subject, as well as from 
the testimony of Cels us and many other remote authors, 
it appears that surgery was incontestably the most 
ancient branch of medicine, the parent of all the rest." 
Hippocrates, then, the father of surgery, let us say, 
gives the Earliest definition of the fractures we are 
about to Study : ? 8. 'Osteov t itpuc ketcii cM.p rip; Kepa^f/Q, f/ to eXkoq 
uvdpujtoQ, Kat ro o^riov Eipi^GiOr/ t^q aapn6c, etc.1 (The bone is broken 
in another part of the head than that in which the man 
received the injury, and the bone was stripped of the 
flesh.) 
This definition remained unimproved until more than 
1 Hippocrates. (Eiivres Completes d'Hippocrate, par E. Littr^. 10 vols. 8vo. 
Paris, 1841. Vol. iii. p. 211. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
7 
two thousand years later, when, in 1873, Felizet sug- 
gested the division of fractures of the cranium into 
" immediate and mediate1 if, indeed, this suggestion 
be an improvement. 
Hippocrates despaired of the cure of fractures remote 
from the seat of the wound, and seems to have had no 
more definite idea about them than that they might 
occur. 
The next author, to whose writings access may still 
be had, who refers to this subject, is Celsus, who lived 
about the beginning of the Christian era. Celsus says : 
" Solet etiam evenire, nt altera parte fuerit ictus, et os 
altera fiderit." (It sometimes happens, also, that the 
blow has fallen upon one point, and the bone is cleft in 
another.) He furthermore recommends cutting down 
upon any point where there is softening and swelling, 
in case no fissure is found at the point struck, and bad 
symptoms arise.2 Here was a decided advance upon 
the teaching of Hippocrates, another being the obser- 
vation of Celsus that the vessels of the brain might be 
ruptured without fracture of the cranium, anticipating 
a much later explanation of the term " contrecoup" 
Soranus3 (97-117 A. D.) says: "Resonantia secundum 
aliquos est facta in calvarias partibus fractura oppositis 
iis quae percussae fuerunt, sine vulnere superpositum." 
Oribasius (about 350 A.D.) says : "Ceterum quae ab 
ipsis dicitur resonantia, rima quaedam est, quae non quo 
fuit ictus, sed adverso loco sit, simili ratione ac in vasis 
1 Felizet, G. Recherches anatomiques et experimentales sur les fractures du 
crane. Paris, 1873. P. 160. 
2 Celsus Aur. Corn. Celsi de medicina libri octo, cum notis integris . . . 
cnra et studio Th. J. ab Almeloveen, etc. 8vo. pp. 749. Ludg. Batav., 1746. 
Lib. viii. De calvaria fracta. 
3 Soranus. De fracturarum signis, etc. Florentiae, 1754. Pp. 46 and 47. 8 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
fictilibus, quae altera parte percussa, in alteram rimam 
accipiunt." 
It is said in many of the more recent works on 
counterstroke that Paul of JEgina (about 500 A. D.) 
denied the occurrence of the fractures at a distant point. 
For this denial, however, he offered an explanation 
which was considered wise when it was suggested as 
original about 1200 years later, namely, that the frac- 
tures attributed to counterstroke are chargeable to 
other blows, received after the first: by a fall, for 
example.1 
The teachings of these great men were but little 
modified in many centuries. 
In 1535 Berengarius discussed most intelligently the 
possibility of a fracture in an opposite part of the skull 
without lesion of the part receiving the blow. After 
going over the ground pretty thoroughly and asserting 
the ease and frequency with which multiple fractures, 
and fractures caused at the opposite side by a fall after 
the blow has been received, may be, and have been, 
misinterpreted, he concludes that he cannot deny that a 
true, independent, opposite fracture may occur.2 
The idea of counterstroke was, so far as my investi- 
gations go, first plainly and unequivocally defended by 
Paw, who, in 1616, says that a blow may fracture not 
only another part of the skull, but even an opposite 
one; thus the forehead being struck, and remaining 
intact, the occiput may be fissured, or when one tern- 
1 Paulus jEgineta. The Seven Books of Paulus ^Fgineta. Translated by 
Francis Adams. Sydenham Soc. London, 1846, 3 vols. Book vi., Sect. xc. 
2 Tractatus perutilis et completus de Fractura Cranii, ab eximio artium et 
medicinse'Doctore D. Magistro Jacobo Berengario Carpensis, etc. 8vo. folii iiii. 
ex. Venetiis, MDXXXV., capitulum ii. ff. x-xiii. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
9 
poral or parietal bone has received the blow, the oppo- 
site one may give way.1 lie also notes a case in which 
he found, at the autopsy, that the outer plate of the 
bone which was struck remained unbroken, while a 
fragment was detached from the inner one and driven 
into the brain.2 
In 1649, Guillemeau expressed doubt as to the occur- 
rence of fractures by counterstroke, which, he says, 
many writers speak of. "Mais," he says, "telle frac- 
ture n'est iamais venue a ma co<nioissance & ne me 
puis persuader qu'elle puisse aduenir, si ce n'est quand 
les sutures sont serrees & vnies ensemble, on perdues 
depuis 1'os frappe, iusques a celuy qui se trouue a 1'oppo- 
site fracture."3 
In the same century Boerhaave recognized the fact 
that the brain may be lacerated or compressed, though 
the skull remains entire, and Van Swieten, in com- 
menting on this statement, explains the phenomenon as 
due to the momentum communicated to the brain, which 
dashes it against the resisting interior of the opposite 
side of the skull.4 Van Swieten also called attention to 
the possible injury of the diploe alone, without fracture 
of either table of the skull.5 
Still in the seventeenth century, Stalpart van der 
Wiel speaks most unequivocally of lesions of the 
cranial contents at a point opposite to that which has 
1 Petri Paaw Amstelodamensis succenturiatus anatomicus continens com- 
mentaria in Hippocratem, de capitis vulneribus, etc. Lugduni Batavorum, 
Ann. MDCXVI. 
' Ibid., p. 108. 
8 Jacques Guillemeau. Les (Euvres de Chirurgie. Folio. Rouen, 1649. De 
la contrafente aux os de la teste, p. 656. 
4 Van Swieten. Commentaries on Boerhaave's Aphorisms. Translation. 
18 vols. 8vo. Edinburgh, 1776. Vol. ii. p. 399. 
5 Ibid., p. 339. 10 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
received a blow, giving this as a justification for tre- 
panning.1 
In 1708, Wagner published a thesis on contrecoup 
in which he quotes Fabricius de Aquapendente (1537- 
1619) as explaining it by the efforts of the air, which he 
supposed the skull to contain, to escape from the side 
opposite to that on which the blow was received. Marcus 
Marci, he says, attributed it to the spheroidal shape of 
the skull and the special violence of the blow.2 
In 1764, Aurran published a paper to show that the 
location of a fracture by contrecoup could be certainly 
detennined. In this paper he calls attention to the fact 
that the sutures of the skull do not set a limit to a frac- 
ture. He claims that the temporal regions are most 
liable to fracture, partly because they are comparatively 
thin, and partly because of their architectural peculiari- 
ties, since they embrace the parietals and are driven 
asunder by blows which fall upon the vault of the 
cranium.3 
Soon after this, occurred a veritable epoch in the his- 
tory of our subject. The Royal Academy of Surgery 
of Paris, which had been founded in 1'631, proposed in 
1760, and again in 1765, as the subject for a prize, the 
following proposition: " To establish the theory of 
counterstroke in lesions of the head; and the practical 
conclusions which may be drawn from it." On the first 
of these occasions the prize was not awarded; on the 
1 Stalpart van der Wiel. Observ. rariorum . . . Centuria prior. 16mo. 
Lugduni Batavorum, 1687. Observ. VII. and comments on it. 
2 Wagner. Sur les Contrecoups. Haller's Collection de Theses. 5 vols., 
12mo. Paris, 1757. Tome i. pp. 11-28. 
3 Aurran. Observations sur les contre-coups, qui tendent a prouver qu'on peut 
decouvrir surement 1'endroit fracture, selon le lieu qui a re?u le choc. Journ. 
de Med., Chir., et Pharmacie, Paris, 1764, tome xxi. pp. 252-260. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
11 
second, it was awarded to Grima,1 who sent in for the 
second time the same essay which he had sent in for the 
former competition, and which had been thought the best 
at that time.2 The same question was proposed for the 
prize of 1768, when prizes were awarded to Saucerotte3 
and Sabouraut,4 for which Chopart5 also presented an 
essay, which was accepted and published by the Acad- 
emy. Chopart not only recognized the elasticity of the 
skull, but exaggerated it, and, as a diagram in his essay 
shows, believed that a blow produced alternating and 
reciprocal shortening and lengthening of the axes, in a 
manner which some authors describe as undulatory. 
Nor would the history of this epoch be complete with- 
out mention of a valuable memoir upon counterstroke in 
other parts than the head,6 written by David, though 
published under the name of his pupil, Bazille-to which 
a double prize was awarded in 1771. 
All of these writers considered the mechanism of frac- 
tures by counterstroke critically. Grima defined con- 
trecoup as an injury inflicted at any point other than 
that to which the violence was applied: fracture of 
the cranium at ' an opposite point-which was often 
spoken of as if it were the only true counterstroke- 
1 Louis. Recueil d'observations d'anatomie et de chirurgie pour servir de base 
a la theorie des lesions de la tete par contre-coup, etc. 12mo. pp. 385. Paris, 
1788. Pp. 13, 37. 
2 Grima. Memoires sur les sujets proposes pour le Prix de PAcademie royale 
de Chirurgie. Tome iv. Paris, 1778. Pp. 246-273. 
8 Saucerotte. Ibid., pp. 368-438. 4 Sabouraut. Ibid., pp. 335-518. 
5 Chopart. Ibid., pp. 519-562. 
6 Bazille. Mem. sur la proposition suivante; Exposer les effets des contre- 
coups dans les differentes parties du corps, autres que la tete, etc. Prix de 
PAcademie royale de Chirurgie. Tome iv. pp. 563-633. 
This essay was translated and published in English in 1789, in the surgical 
tracts of the late J. O. Justamond, F.R. S.,etc., edited by Mr. William IIouls- 
ton-4to., London, 1789. 12 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
being only one form of it; and he included under his 
definition injuries of the contents of the cranium without 
fracture of the bony part. All this, it will be seen from 
what I have stated above, had been more or less imper- 
fectly laid down long before; but it was not until the 
epoch of which I am now speaking that it was clearly 
formulated. Grima insisted upon considering the skull 
as one piece after the sutures had closed, a very impor- 
tant matter in regard to the mechanism of fractures in it. 
He also calls attention to the possibility that a fracture 
attributed to counterstroke has been caused by a fall 
after a blow, a point in regard to which, as we have seen, 
Paul of JEgina referred 1200 years before. Grima 
compared fracture of the cranium by contrecoup to that 
which occurs in a stone-wall, which, when struck at one 
point, may break at another. He divides contrecoup into 
seven kinds, one being that in which the contents of 
the skull alone are lacerated. He speaks of Valleriola 
as having recognized a contrecoup by the occurrence 
of a gangrene at the side opposite to that which had 
received the blow, and of Bartholini as having drawn 
the same conclusion from the presence of an abscess. 
Grima, finally, advises trepanning at the suspected 
point, when symptoms arise which cannot be accounted 
for by the local injury, claiming that if it proves useless, 
it can, at least, do no harm. 
Saucerotte adopted practically the same definition of 
contrecoup as did Grima: " A lesion produced by a 
blow in another place than that which received the 
blow." He makes eight kinds of counterstroke, one of 
them involving the diploe alone. In explaining the 
mechanism of counterstroke, he considers the skull as a 
solid case, which, in its vertical section, presents the MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
13 
appearance of a scalene triangle. He dwells upon the 
varying degrees of thickness and strength in its differ- 
ent parts, and claims that its fractures are due to over- 
cur vation and to flattening-. In this he foreshadows a 
theory of which I shall speak hereafter, as well as in the 
further statement that when the skull is struck it 
"undulates" and changes its shape "alternatively." 
The vibration theory, involved in comparisons of the 
skull to a wall, as done by Grima, or to a glass or clay 
vase, which was a very ancient comparison, he rejects. 
He lays stress on the very important point that the 
skull contains fluid contents which are extremely incom- 
pressible, holding that a blow sets in motion a column 
which is practically solid and which strikes with great 
violence the opposite side-a conclusion which contains 
a fatal error, since the laws of hydrostatics make it clear 
that such a force is transmitted equally in all directions. 
Finally, he directs attention to a point which should 
never be overlooked, namely, a due appreciation of the 
character and direction of the force which effects the 
injury. Among his practical conclusions, one is to 
trepan more boldly than some surgeons think advisable 
nowadays, and another is to cut into the brain itself in 
certain cases. 
Sabouraut speaks of the skull as a spheroidal case 
which cannot break without changing its shape. Under 
the influence of a blow, he says, its diameters lengthen 
and shorten, and shorten and lengthen alternately-a 
statement which would appear to be inverted unless it 
be understood to refer to the diameter perpendicular to 
the direction of the blow, in which case it fits exactly 
the theory already alluded to as to be spoken of here- 
after. He explains the physics of the skull, as he under- 14 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
stands them, quite thoroughly, and acknowledges the 
difficulty of making a practical application of the in- 
formation which an understanding- of them might be 
expected to afford. 
Chopart describes the skull as an elliptical case, and 
divides contrecoup into eight varieties, similar to those 
already referred to. He also calls attention to the frac- 
tures produced by falls upon the buttocks, knees, or 
feet, and classes them under the heading- of counter- 
stroke. 
The essay of David, mentioned together with those 
we have been citing, is interesting as showing the extent 
to which in those days the idea of counterstroke was 
stretched, for it includes a number of fractures which 
are nowadays attributed to muscular action, as well 
as injury of the contents of the pelvis, abdomen, and 
thorax by the concussion due to falls. 
In 1773, Mehee de la Touche published a valuable 
monograph on counterstroke1 in which the same broad 
definition of it is given, namely, "a lesion produced by 
a blow at another point than that which was struck." 
The opposite point he considers the most frequent seat 
of counterstroke, that occurring elsewhere he attributes 
to special weakness of the part which yields. From the 
consideration of counterstroke he goes on to that of its 
symptoms, and is led into an interesting discussion of 
cross-paralysis, in regard to which he records some in- 
structive experiments on dogs. This subject had 
attracted attention since the earliest times of medicine, 
and had been very sagaciously studied in the beginning 
1 Mehee de la Touche. Traite des lesions de la tele par contre-coup. Small 
8vo. pp. xix. 264. Meaux, 1773. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
15 
of the 18th century by Parfour de Petit,1 whose experi- 
ments on doo's were of the most interesting and inge- 
nious character. 
It was not until the beginning of the present century 
that I find any noteworthy reference to the mechanism 
of fractures of the cranium in England, when Sir Charles 
Bell2 compared the movements of the cranium under the 
influence of a blow to those of a bell, and illustrated his 
views by an experiment in which he placed two balls inside 
of, and touching a hoop, one at each pole of the direction 
of the blow to be applied, and two more outside of, and 
touching it at the poles of the transverse diameter. On 
striking the hoop, the two balls in the line of the force 
are driven toward the centre, while the two balls at the 
poles of the transverse diameter are driven away from 
it. This shows that a blow shortens the diameter par- 
allel to the direction of the force and lengthens that one 
perpendicular to it-another foreshadowing of the theory 
already referred to and to be described hereafter. 
In 1828, Mr., afterward Sir, Benjamin Brodie3 accepted 
the current theory of counterstroke, and described the 
fractures caused by the impact of other bones on the 
cranium. 
In 1844, Aran published an exceedingly valuable 
paper on fractures of the base of the skull,4 in which he 
1 Petit. Nouveau Systeme du Cerveau. Extrait des Lettres d'un Medecin des 
Hopitaux du Roi a Namur (Parfour de Petit.) In Louis: Recueil d'observa- 
tions d'anatomie et de chirurgie pour servir de base a la th^orie des lesions de la 
tete par contre-coup, etc. 12mo. pp. 385. Paris, 1788. 
2 Sir Charles Bell. Surgical Observations. 2 vols. 8vo. Edinburgh, 1816. 
Vol. i. pp. 461-489. 
3 Brodie, B. C., F.R.S. Pathological and Surgical Observations relating to 
Injuries of the Brain. Medico-Chirurgical Transactions, 1828, vol. xiv. pp. 
325-423. 
4 Aran, F. A. Recherches sur les fractures de la base du crane. Arch. g5n. 
de Med., 4 ser., tome vi. pp. 180-209, 309-347, Paris, 1844. 16 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
formulated a theory which has been known by his name 
ever since. This theory was, that fractures of the base 
are always connected with fractures of the vault, from 
which they radiate, following a line within the zone in 
which the former occurred, and taking a course which 
corresponds with shortest route to the base. Uis 
conclusions are formulated as follows : 
1. Ue never saw a fracture of the base, caused by a 
blow, without a direct fracture. 
2. Fractures of the vault joined the base by " irradia- 
tion," and crossed any sutures in their way. 
3. They followed the shortest route to the base (the 
curve of shortest radius). 
4. They were ordinarily limited to certain regions 
(corresponding to the several great fossae of the cranium), 
and followed a certain direction. 
5. Fractures of the vault sometimes coincide with 
independent fractures of the base; but only when there 
is considerable comminution (Sbranlement) and very mul- 
tiplied fractures. 
These conclusions of Aran rested upon the results of a 
large number of experiments, upon fresh and dry skulls, 
by blows with very heavy hammers, and by throwing them 
down upon a hard pavement, as well as experiments in 
which he pitched entire bodies down upon their heads 
after having made the legs rigid by binding them to a 
strong iron bar. Certain writers have assumed that 
his experiments numbered one hundred. The only 
ground which I can find for this assumption is his 
statement that indirect fractures of the base by irra- 
diation constitute 99 per cent, of the whole number-a 
statement which furnishes no clear indication as to the 
number of his experiments. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
17 
Ill 1847, Guthrie1 published a monograph on injuries 
of the head, which is unsurpassed in the English lan- 
guage, in which he gives an excellent resume of the his- 
tory of various sorts of fractures of the cranium. Among 
them he speaks of counterstroke, the occurrence of 
which from temporal to temporal, or from parietal to 
parietal, he doubts, but says that fracture of the base 
from blows on the vertex or occiput are among the com- 
monest accidents of surgery. Except for an uninter- 
preted reference to a statement of Chopart (q. v.), he 
expresses no opinion whatever as to their mechanism. 
In 1853 was published, in Guy's Hospital Reports, a 
first instalment of Mr. Hilton's sagacious lectures on 
the cranium,2 which was followed, in 1855, by their 
publication entire in a separate volume, by Dr. Pavy, 
after their revision by Mr. Hilton himself.3 
In these lectures Mr. Hilton explains fractures of the 
skull upon the "vibration-theory," and speaks of the 
posterior clinoid processes and the extremities of the 
petrous bone as points to which vibrations are conducted, 
and where they are transmitted to the cerebro-spinal 
fluid, thus being "interrupted or lost before reaching 
the cerebral tissues," etc. The fallacy of this conclusion 
I shall have to consider hereafter, citing Mr. Hilton's 
opinions here for their historical interest. 
In 1854 the keynote to a new theory of indirect 
1 Guthrie, G. J. On Injuries of the Head, etc. 4to. pp. vi. 155. London, 
1847. 
2 Hilton, John. Notes on the Development and Design of Certain Portions of 
the Cranium. Four Lectures by John Hilton, F.R.S. Collected by F. W. Pavy, 
M.B. Guy's Hospital Reports, 1853, pp. 357-400. 
3 Hilton. Notes on Some of the Developmental and Functional Relations of 
Certain Portions of the Cranium. Selected by Frederick William Pavy, M.D., 
London, from the Lectures on Anatomy, delivered at Guy's Hospital, by John 
Hilton, F.R.S. 8vo. pp. 93, with 9 plates. London, 1855. 18 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
fractures of the skull-which had, however, as we have 
seen, been foreshadowed much earlier by certain ob- 
servers-was struck in Germany by experiments made 
by Bruns,1 of Tubingen, to determine the elasticity of 
the cranium. 
In 1858, Mr. Prescott Hewett published a series of 
lectures on the anatomy, injuries, and diseases of the 
head, in which is contained an exceedingly full and able 
discussion of fractures of the cranium. He thought 
fractures by contrecoup to be rare, though he says that 
" indirect fractures " of the base are very common. As 
to the general law which governs the location and extent 
of fractures of the cranium, he accepts the views of 
Aran.2 
In 1864, Chauvel published a thesis on fractures of the 
cranium,3 founded upon a careful study of its anatomy, 
in which he laid great stress upon the elasticity of the 
skull, and described the "vibrations" produced by a 
blow, as the repeated and alternating shortening of the 
prime axis and lengthening of the transverse axis. He 
called attention to the fact that the petrous bone, although 
the hardest in the cranium, is the one most frequently 
fractured. He described three kinds of fractures : 1, 
direct; 2, contra-direct; 3, indirect. The first kind is 
simple enough. The second occurs opposite to the point 
struck, and he offered no explanation for it, except the 
comparison of fractures caused by the spinal column to 
the manner in which the handle is driven into the head 
1 Bruns. Die chirurgischen Krankheiten und Verletzungen des Gehirns, etc. 
Tubingen, 1854. 
3 Hewett, Prescott. Lectures on the Anatomy, Injuries, and Diseases of the 
Head. Med. Times and Gazette, 1858, vol. xvii. pp. 311, 312. 
5 Chauvel, F. Essai sur les fractures du crane. These de Paris, 1864. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
19 
of a hammer by striking the remote end of the handle 
against some resisting body. The third form of fracture 
he defined as that occurring between the point struck 
and that directly opposite. This he found in 11 out of 
60 fractures. 
In 1872, Schwartz analyzed 115 cases, in most of 
which the history was very incomplete, and he found 
fracture of the base alone, without fissure of the con- 
vexity, only 7 times. lie found about 39 per cent, of frac- 
tures limited to the zones described by Aran and Hewett; 
while in over 60 per cent, this regularity was wanting. 
[Hewett's figures were about the same, though his 
conclusions were different.] This is one of the most 
important features of his investigations. Another is 
that a study of the fractures he had analyzed showed 
that the petrous bone was fractured in 66 out of 115 
cases; and that force applied to the side of the head 
caused fractures somewhat parallel to the axis of the 
bone, while force applied to the occiput, or forehead, 
or vertex, caused fractures transverse to the axis.1 This 
was an important contribution to the accumulating 
material for a new consideration of the mechanism of 
indirect fractures of the skull, as we shall see hereafter. 
In 1873, Felizet published an elaborate illustrated 
monograph on the subject of fractures of the cranium, 
which, with the paper of Aran, may be regarded as among 
the most important contributions to the literature of the 
subject up to that time.2 He regards this as a solid 
case, of a spheroidal shape, but claims that its internal 
1 Schwartz, Arnold. Zur statistik der Fracturen der Schadelbasis. In. Diss. 
8vo. pp. 52. Dorpat, 1872. 
2 Felizet, G. Recherches anatomiques ct experimentales sur les fractures du 
crane. 8vo. pp. 167. Paris, 1873. 20 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
configuration renders inaccurate a comparison of it to 
any geometrical figure whatever. By experiment he 
demonstrated that the dura mater makes the skull where 
it is attached more resistant to fractures caused by flatten- 
ing its curve. Experimenting with a billiard ball let fall 
from a height, he found that its equator was increased, 
that this increase was greater in a direction at right angles 
to its fibres than in a direction parallel to them. The 
result was an ellipsoidal equator, and when a fracture 
occurred, this crossed the long diameter at right angles 
(p. 72). lie unwittingly paraphrases the theory to 
which I have several times alluded, and which I shall 
soon consider, in saying, "We know that a fracture 
results from depression of the curved surface situated 
between two resisting pieces, and we know, also, that 
every effort tending to depress this curve divides into two 
forces, the one a driving force force de tassement}, which 
acts on the axis, or near to it, of the supporting walls; 
the other, a disruptive force {force de glissemenf which 
acts transversely to them, and tends to separate the two 
extremities of these pieces " (p. 108). Again (p. 139), he 
compares the separation of sutures, the result of blows, 
to that which is effected in anatomical preparations by 
filling the skull with dry peas, and then soaking them, 
so that by swelling they tear the skull apart. lie declares 
that there is a perfect analogy between this and what 
he calls the " grand fracas" (grand smash), in which 
he says "the bones, compressed over a large surface, 
rock fasculent), and this rocking movement sets up 
violently a dragging force perpendicular to the plane of 
the surface of union of the bones of the cranium." As 
we shall see hereafter, this is the same as saying that a 
force which depresses an elastic curved figure, will MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
21 
enlarge its diameter, and be converted into a disruptive 
force acting at right angles (perpendicular) to the 
meridian. Herein Felizet comes near to the theory 
which the Germans call the "Berstungs" theory, 
although he does itot quite reach it, and may perhaps, 
even now, not see his statements to be so strong a 
confirmation of it as they appear to me to be. 
The term "contrecoup" Felizet rejects, and would adopt 
that of M. Beau, of Brest, who called indirect fractures 
"mediate." Felizet compares the mechanism of these 
fractures to those produced by a blow upon a wedge or 
a chisel. The part broken, he holds, is directly struck 
by another part, which, in its turn, received a blow and 
transmitted it. Yet he admits that, very rarely, these 
fractures by contrecoup do occur (p. 156). He divides 
fractures of the cranium into direct, indirect, and mixed. 
Indirect fractures include those which are independent. 
In respect to the application of the violence which causes 
them, fractures may be divided into immediate and me- 
diate (pp. 159, 160). His conclusions may be briefly 
stated as follows : all fractures not immediately limited 
to the point of impact follow certain definite routes, to 
which they are restricted by the added strength of cer- 
tain parts of the skull, which depends upon the presence 
of certain "murs boutants" (buttresses): the petrous 
bones, the orbito-sphenoid prominences, the occipital 
protuberance, and the naso-frontal protuberance. The 
basilar process and the antero-lateral parts of the occi- 
pital bone remain intact amid all fissures and constitute 
a "centre of resistance." The vibration theory, he says, 
is disproved by experiments, the fundamental phenome- 
non is a violent flattening of part of the vault, and a 
separation of the resisting portions {pieces de resistance} 22 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
which support it. When the violence is perpendicular 
to the surface of the cranium, fractures radiate directly 
to the base. In this, it will be seen, Felizet agrees with 
Aran. Finally, he admits that there are fractures, called 
by "contrecoup" the mechanism of which escapes us 
completely (pp. 161-164). 
The opinions of Felizet are founded upon a careful 
analysis of a number of pathological specimens and 
upon a number of experiments upon fresh skulls. The 
value of his work can be appreciated only after a thor- 
ough study of it. The result of it was to bring him to 
a conclusion which may be succinctly stated as that in- 
direct fractures are due to a disruption by splitting. 
There can be no doubt that the course of a fracture will 
be determined to a considerable extent by the reinforce- 
ments which the skull has, in certain places, from its 
buttresses (murs boutants); but, as we shall see hereafter, 
these very buttresses are often broken both transversely 
and longitudinally, and Felizet's centre of resistance is 
by no means a centre of immunity, but an exceedingly 
frequent seat of fracture. 
A few years later-for events now crowd upon each 
other in the history of fractures of the cranium-Baum1 
opposed the vibration theory, and made some experi- 
ments by strewing sand on a skull and applying a 
vibrating tuning-fork to it. From these experiments he 
concluded that vibrations were restricted by surround- 
ing less elastic parts, like the vibrations of a drum- 
head. The petrous bone, however, he concluded, owing 
to its anatomical structure and relations, vibrates like a 
rod held by one end in a vice. He refers to Weber's 
1 Baum, W. Beitrage zur Lehre von den indirecten Schadelfraeturen. Lan- 
genbeck's Arehiv f. klin. Chir., Bd. xix. S. 381-399, 1876. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
23 
wave theory, and concludes that blows upon the skull 
do not furnish the conditions of repeated impulses which 
produce a high vibratory action. By compression of a 
few skulls in a suitable frame he got results which corre- 
spond to those of later German experimenters, who 
adopted the "bursting" theory. 
In 1878, P. Bruns attributed indirect fractures to the 
elasticity of the skull, as described by v. Bruns in 
1854, and explained the frequent occurrence of these 
fractures in the base of the skull by the fact that this is 
the weakest and most fragile part of it.1 
In the same year, Perrin made some very instructive 
experiments, in which he attempted to imitate the usual 
conditions of the skull by protecting it with an elastic 
cushion of cotton wadding or of caoutchouc and then 
throwing it upon a stone pavement, or by putting the 
cushion on the pavement itself. He always got direct 
fractures by blows, and by precipitating the skull he 
usually got indirect fractures. He showed typical speci- 
mens to the Societe de Chirurgie, in all of which the 
fractures were indirect and meridional, and in some inter- 
esting cases the vitreous alone was involved in certain 
places. He found that blows on the vertex or occiput 
usually cause fractures by contrecoup (which he defines 
as fractures occurring at a place other than that struck), 
direct fractures being rare exceptions; while blows on 
the forehead, the parietals, or the temporal bones, rarely 
cause any but direct fractures.2 
In 1880, Bergmann published another valuable con- 
1 Bruns, P. Die allgemeine Lehre von den Knochenbruchen. Deutsche 
Chirurgie, Lief. 27, 1 Halfte. 
2 Perrin, Maurice. Les fractures du crane par contre-coup. Bull. et. mem. 
de la Soc. de Chir., 1878, pp. 128-136. 24 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
tribution to this subject.1 He compared the elastic 
conditions of the skull to those of the thorax, which, 
when compressed or struck in one part, breaks in another. 
He also compares the mechanism of fractures of the 
skull to the bursting of the eyeball under pressure, 
referring to Arlt's demonstration2, that when compressed 
the eyeball bursts in the equator. Fractures from severe 
blows, he believes, follow this law; those dependent 
upon moderate force follow the law laid down by Felizet. 
He analyzes the statistics of Prescott Hewett and of 
Schwartz, already referred to, and finds that a majority 
of their cases did not follow Aran's law. He calls 
attention to the importance of duly estimating the vari- 
ations in amount, direction, and velocity of the force 
applied to the skull, and the support afforded by 
strengthening bones of the skull and face. He cites 
Baum (whom I have cited) as refuting the vibration 
theory, and seems to have the idea that indirect fractures 
of the skull are to be attributed to a disruptive force, 
and not to a propagation of vibrations. 
In 1880, Messerer3 conducted a series of experiments 
which demonstrated more accurately than had ever been 
done before the elasticity of the cranium, and which 
made clear the fact that when the skull is compressed in 
one axis, the circumference at right angles to it is en- 
larged. 
In 1881, Nicolai Hermann published an inaugural 
dissertation on fractures of the base of the skull, in 
1 Bergmann. Die Lehre von den Kopfverletzungen. Deutsche Chirurgie 
(Billroth and Luecke), Lief. 30. Stuttgart, 1880. 
2 Arlt. Die Verletzungen des Auges mit besonderer Rucksicht auf deren 
gerichtsartzliche Wurdigung. 1875. S. ii. 
8 Messerer. Ueber Elasticitat und Festigkeit der menschlichen Knochen 
Stuttgart, 1880. Cited by V. Wahl, q. v. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
25 
which, besides an analysis of 75 cases gathered from 
various sources, he gives an account of 17 experiments 
in which he compressed the skull in longitudinal, trans- 
verse, and diagonal directions, until it broke. His 
experiments always resulted in a fracture parallel to the 
direction of the compressing force. He believes that 
fracture always begins at one of the points compressed 
and travels away from it. By analyzing the cases he 
had collected he concluded that they supported his 
deductions from experiments! It seems to me that 
some of his figures show plainly that the fissures must 
have begun at the middle and travelled both ways. 
In the same year Julius Schranz published an account 
of 3d experiments upon skulls, some (13) from which 
the vault had been removed, but the most of them 
entire, in which he endeavored to imitate the conditions 
in which fractures are caused by different sorts of vio- 
lence. The experiments were interesting and instruc- 
tive. The great majority of the fractures he produced 
were splitting fractures, and not immediately connected 
with the point to which the violence was applied. In a 
considerable number isolated pieces of the vitreous table 
were split off, or the dorsum ephippii. These (and 
other indirect fractures), he says, can only be explained 
by the vibration theory. A curious result of his experi- 
ments was that the brain was injured only once, and the 
dura mater separated from the bone only three times !2 
But it remained for von Wahl,3 in 1883, to utilize 
1 Hermann, Nicolai. Experimentelle und casuistische Studien uber Fracturen 
der Schadelbasis. Inang. Diss. 8vo. pp. 67, 23 plates. Dorpat, 1881. 
2 Schranz, Julius. Untersuchungen uberdas Entstehen von Schadelbruchen. 
Mediz. Jahrbiicher (Wien), 1881, pp. 291-314, with 5 lithographic plates. 
3 Wahl, Ed. von. Ueber Fracturen der Schadelbasis. Volkmann's Samm- 
lung klin. Vortrage, No. 228. 8vo. pp. 26. Leipzig, 1883. 26 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
the material which had been recently gathering, and to 
formulate unequivocally the theory that fractures of the 
skidl may be divided into: 1, crushing fractures, in 
which the line of fracture runs at right angles to the 
axis of the force applied; and, 2, bursting fractures, in 
which the lines of fracture are parallel to the axis of the 
force which gives rise to them, and which begin, in the 
words of Messerer, at some point in a line which, like 
the equator, in relation to the poles of the earth, cir- 
cumscribes the hollow figure in a plane equally distant 
from both points of compression. He claims that, in com- 
pression of the skull-which may be gradual, as in a vice, 
or sudden, as when effected by a fall or blow-its elas- 
ticity, in toto, comes into play, and while its diameter 
which is parallel to the force applied is shortened, its 
diameters which lie at right angles to this are length- 
ened. The result is, that indirect fractures run in lines 
which we may describe as meridional. His conclu- 
sions rest not only on theoretical considerations and a 
review of the testimony and opinions of others, but also 
upon his own clinical experience, and a series of inge- 
nious experiments, which are fully described and beau- 
tifully illustrated in his monograph, a careful study of 
which may, without injustice, be said to be indispen- 
sable to one who would form a correct opinion upon the 
subject of which it treats. 
In 1881, Dr. Nancrede, of this city, published an 
elaborate and valuable paper on "Injuries of the Head,"1 
in which he adopts the vibration theory, and supports 
his opinions with some interesting anatomical and 
1 Nancrede, Charles B. Injuries of the Head. International Encyclopa?dia 
of Surgery. Edited by John Ashhurst, Jr., M.D., etc. New York, 1884. 
Vol. v. pp. 1-109. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
27 
physical considerations. Ue regards the base as a 
stronger part of the cranium than the vault (pp. 30 
and 32), speaks of the brain as lying on a water-bed 
(p. 31), and describes vibrations of the bones as travel- 
ling by the nearest "anatomical" route to the base, 
there to be discharged, like electricity, at certain points- 
the ends of the petrous bones and the clinoid processes 
-into tissues which are non-conductors of vibration. 
Ue also calls attention to the important influence which 
the position of the head has upon the direction in which 
a force applied to the condyles will be conducted. In a 
very interesting case, which he cites from his own 
experience, there was a separation of the masto-occipital 
suture, which he says was forced apart "as if from 
within." 
In 1884, Messerer published a second and most ad- 
mirable paper on fractures of the cranium,1 in which he 
gives a description and analysis of eighty-two experi- 
ments on fresh skulls, sometimes on entire cadavers. 
His experiments included accurately regulated blows 
upon skulls, detached or resting on the spinal column, 
and falls of the skull upon a hard base. These experi- 
ments completely refute the laws of Aran as well as 
those of Felizet, and seem to show conclusively that 
indirect fractures of the skull are dependent upon sepa- 
ration of the meridians caused by the depression pro- 
duced at the point of contact by a blow. 
Finally, our sketch of the history of this subject is 
brought down to the present year by a reference to the 
1 Messerer, Otto. Experimentelle Untersuchungen uber Schadelbriiche. 8vo. 
pp. 36, with 8 plates. Munchen, 1884. 28 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
interesting and beautifully illustrated paper of Greder, 
published in the early part of 1885? 
The experiments of Greder were made upon skulls 
connected with the trunk and still covered with their in- 
teguments and containing the brain, by blows with a 
weight of 6400-7650 grammes (about 12-15 pounds). 
After a large number of these experiments, some of which 
were most ingeniously varied, Greder comes to the conclu- 
sion that solutions of continuity of the base of the skull 
are to be regarded as the result of bursting; that the 
direction of all fissures is parallel to that of the force 
causing them; that the extension of a fissure is depen- 
dent upon so many intercurrent conditions peculiar to 
each skull, that it can at most be only suspected from the 
intensity of the violence (p. 509). As to the point at 
which the burst begins, he holds that it is not always 
in the equatorial line, nor always at the point of impact, 
but at that point where resistance to the disruptive 
force is least. This will happen, he thinks, in the majority 
of cases, in the equator or in its neighborhood (p. 506). 
The Elastic Properties of the Skull. 
From the preceding sketch, it will be seen that those 
who have thoroughly investigated the mechanism of 
indirect fractures of the skull have been led to conclu- 
sions which establish a great importance for its elastic 
properties. These properties, as we have seen, were 
first clearly enunciated about the middle of the last 
century by Saucerotte, Sabouraut, and Chopart, in their 
1 Greder, Wilhelm. Experimentelle Untersuchungen uber Schadelbasis- 
bruche. Deutsche Zeitschrift fur Chirurgie, Bd. xxi., 5 und 6 Hefte, 9 Marz, 
1885, S. 491-510, tafeln vii.-xiv. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
29 
essays for the prize of the Academy of Surgery of Paris. 
In the beginning of this century, Sir Charles Bell illus- 
trated them by an ingenious physical experiment. In 
1851, von Bruns demonstrated them by a series of ex- 
periments which only required multiplication and varia- 
tion to confirm what an important part the elasticity of 
the skull plays in the production of indirect fractures. 
Since then, almost innumerable experiments and studies 
of specimens of fractures of the skull have cooperated 
to establish the conviction that, with certain exceptions, 
the mechanism of indirect fractures of the skull may 
reasonably be explained according to what the Germans 
call the "bursting" theory-that is, to the conversion of 
direct depressing force into an indirect disruptive force, 
brought about by a shortening of the axis parallel to 
the direction of the force and a complementary lengthen- 
ing of the axes at right angles to the former. A mass 
of evidence in support of this view is now accessible to 
any one who cares to examine it. It would not be pos- 
sible to lay it all before you; so I shall select what I 
think most suitable to this occasion, and ask your atten- 
tion to certain results obtained by Messerer, whose 
experiments in this connection have been very numerous 
and may be regarded as typical. In doing this, I intend 
no reflection upon the admirable work of Aran, von 
Bruns, Felizet, Baum, Perrin, Hermann, Schranz, von 
Wahl, and Greder, which must be studied to be suffi- 
ciently appreciated. 
The experiments of Messerer can be analyzed so as 
to throw a great deal of light upon the physical prop- 
erties of the skull, revealing the parts in which it is 
strongest, and those in which it is weakest. 
But, in order to understand their significance, we 30 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
must have a clear idea of the mechanism by which, in a 
hollow case, the shape of which has a general resem- 
blance to that of a spheroid or ellipsoid, a compressing 
force is converted into a disruptive force. It will be 
readily seen that when an elastic spheroid is com- 
pressed in any diameter, all the diameters lying at right 
angles to this-that is to say, in planes parallel to that 
of the equator-must be elongated. The experiment of 
pressing on the convex side of a bow, the ends of which 
rest on the ground, will illustrate what takes place in 
every chord of every arc that is depressed. (See Fig. 1.) 
Fig. 1. 
When a force is applied to A so as to shorten the axis AB to AZB, the axis 
CD will be lengthened to C'D', and the compressing force in the line AB is 
converted into a disruptive force acting at right angles to this-that is, in the 
line CD. 
It is equally clear that the elongation of the diameters 
lying in any plane will elongate the circumference of this 
plane, because a circumference of longer radius is longer 
than a circumference of shorter radius. As a result of 
this elongation of the circumferences parallel to the 
equator in any spheroid or ellipsoid, the meridians pass- 
ing from pole to pole will be separated in a direct ratio 
to the extension of the different diameters and circum- 
ferences. This operation is illustrated whenever an MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
31 
umbrella is raised. (See Fig. 2.) Asa consequence of 
the separation of the meridians in a hollow sphere or 
ellipse, particles which before occupied a certain space 
between two meridians, will be compelled to separate in 
order to occupy the increased space between the meridians. 
The consequence will be that, in every case such as we 
have supposed, there will be a struggle between the co- 
hesion of the particles and the disruptive force due to the 
separation of the meridians, and whenever the disruptive 
Fig. 2. 
When in a spheroid a force is applied to A so as to shorten the axis AB to 
AZB, all the axes at right angles to it are lengthened, and the circumference 
of any plane in which they lie will be lengthened, as CED to CZE<DZ, and the 
meridians passing round the spheroid will be separated. Thus the direct de- 
pressing force is converted into a disruptive force acting at right angles to it. 
force overpowers the cohesion of the particles lying 
along and between two of the meridians, a solution of 
continuity will take place. The disruptive force will 
be at a maximum at the equator, but the same con- 
ditions of disruptive force opposed to cohesion will be 
found in different proportions in every line parallel to 
the equator. As a result, in a perfect sphere with 
homogeneous walls such a solution of continuity would 
naturally begin at the geometrical equator and extend 
equally and simultaneously in opposite directions in a 32 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
meridional line toward the poles. Bnt in a spheroid or 
ellipsoid not regular in shape, and with walls varying 
in strength in different parts, the result would be modi- 
fied by these variations. This is exactly what we find 
in the case of the skull, which, while bearing a certain 
resemblance to an ellipsoid, does so in only a modified 
way, and can only be expected to exemplify the law 
just stated subject to modifications due to its own 
peculiarities. 
With this in mind, let us see what the experiments of 
Messerer show. Messerer found that the skull burst in 
the base under an average pressure of 650 kilogrammes 
applied in a longitudinal direction, and under an average 
pressure of 520 kilogrammes applied in a transverse 
direction. From this we may draw two very important 
deductions. First, because the burst took place in the 
base: 
Corollary I. The cohesive power of the base of the 
skull is less than that of the vault. 
Second, because the skull burst under a pressure of 
529 kilogrammes applied transversely, and under a pres- 
sure of 650 kilogrammes applied longitudinally: 
Corollary II Cohesion is less in the coronal zone of 
the skull than in the sagittal zone-that is to say, the 
skull is less able to resist a disruptive force due to blows 
upon the vertex or sides in the coronal zone than it is 
to resist a similar force caused by blows applied to the 
forehead or occiput. This is not only a fair inference 
from the experiments of Messerer, but it also accords 
with clinical observation.- 
Messerer found again that compression of the skull in 
a transverse direction, with a force of 520 kilogrammes, 
diminished the transverse diameter 4.4 millimetres; and MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
33 
that compression in a longitudinal direction, with a force 
of 650 kilogrammes, diminished the longitudinal diam- 
eter only 2.7 millimetres. From this wTe may deduce 
Corollary III. The skull is more compressible in the 
transverse diameter than in the longitudinal diameter. 
(This fact tends to strengthen the deduction of Corol- 
lary II.) 
Messerer found, also, that compression of the skull in 
the transverse diameter, with a force of 520 kilogrammes, 
increased the longitudinal diameter 0.4 millimetre, and 
the perpendicular diameter 0.6 millimetre. From this 
we may deduce 
Corollary IC. The skull is more extensible in the per- 
pendicular diameter than in the longitudinal diameter of 
the sagittal zone. The natural inference from this corol- 
lary is that, under the influence of a force applied to the 
sides of the head a fracture which would naturally begin 
in some point in the sagittal zone, will begin in that part 
of it which is intercepted by the perpendicular diameter 
more readily than in that part of it which is intercepted 
by the longitudinal diameter-that is to say, at the base 
or vertex rather than at the forehead or occiput. We 
have already seen (Corollary I.) that the cohesion of the 
skull is less at the base than in the vault, therefore: of 
the two points just indicated, the base is that of election. 
Here, again, clinical observation supports our deduction. 
Messerer found, further, that compression of the skull 
in the longitudinal diameter with a force of 650 kilo- 
grammes increased the transverse diameter 0.6 millimetre, 
and the perpendicular diameter 0.1 millimetre. From 
this we may deduce 
Corollary V. The skull is more extensible in the trans- 
verse diameter than in the perpendicular diameter of the 34 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
coronal zone. (This is the converse of Corollary III.) 
The natural inference from this corollary is that, under 
the influence of force applied to the forehead or occiput, 
a fracture which would naturally begin at some point in 
the coronal zone will begin in that part of it which is 
intercepted by the transverse diameter more readily than 
in that part of it which is intercepted by the perpendicular 
diameter-that is, at the sides rather than at the base or 
vertex. We have already seen (Corollary I.) that cohe- 
sion is less in the base than in the vault; therefore, a 
fracture which, for the reasons just stated, would natur- 
ally begin at the side of the skull would be more likely 
to occur near the base than near the vertex. In estimat- 
ing this probability it may also be borne in mind that 
the horizontal equator of the skull lies nearer to the base 
than to the vertex, the curvature of the former being 
much less than that of the latter: so that the point of 
election for the fractures we are now discussing would 
naturally lie low down on the side of the skull. This 
deduction also is supported by clinical observation. 
Messerer found, again, that compression of the skull in 
the transverse diameter, with a force of 520 kilogrammes, 
increased the longitudinal diameter 0.4 millimetre and 
the perpendicular diameter 0.6 millimetre; and that 
compression of the skull in the longitudinal diameter 
with a force of 650 kilogrammes, increased the transverse 
diameter 0.6 millimetre and the perpendicular diameter 
0.1 millimetre. From this we may deduce 
Corollary VI. The skull is more extensible along the 
sagittal equator than it is along the coronal equator. We 
have already seen (Corollary III.) that the skull is more 
compressible in the transverse diameter than it is in the 
longitudinal diameter. It is, therefore, seen that the equa- MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
35 
tor along which the skull is more extensible (the sagit- 
tal) is that one the plane of which is cut at right angles 
by the diameter in which it is more compressible (the 
transverse), and vice versa ; which furnishes in the skull 
a demonstration not only of the elongation of the equa- 
tor which is produced by depression of the poles of a 
spheroid, but also of the direct ratio of this elongation 
to the depression. Furthermore, it appears from the 
observation of Messerer just cited, that a smaller force 
applied to the skull in a transverse direction will produce 
a greater elongation of the corresponding equator than 
will be produced by the application of a decidedly greater 
force in a longitudinal direction. From this we may 
draw the deduction that force applied to the side of the 
head is more likely to produce a fracture crossing the 
sagittal equator than force applied to the forehead or 
occiput is to cause a fracture crossing the coronal equa- 
tor. This deduction is in accord with the results of 
Messerer's experiments, in which the skull burst under 
a pressure of 520 kilogrammes applied in a transverse 
direction, and only under a force of 650 kilogrammes ap- 
plied in a longitudinal direction. It is also in accord 
with clinical observation. 
We have now analyzed Messerer's experiments so as 
to ascertain the points of election for disruptive fractures 
which may occur in (that is, across) two of the principal 
equators of the skull, the sagittal and the coronal. It 
is not possible to discover in the same way the points of 
election in the horizontal equator of the skull; for Mes- 
serer found that compression of the skull in the vertical 
direction, between the vertex and the spinal column, led 
to a direct driving in of the base under so small a pres- 
sure as 270 kilogrammes. 36 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
The results of our analysis of these experiments may 
be summarized as follows : 1. Bursting fractures are 
more likely to occur at the base of the skull than in the 
vault. 2. Force applied to the side of the head may be 
expected to produce a bursting fracture crossing the 
sagittal equator. Such a fracture is more likely to occur 
in the base than at the vertex. 3. Force applied to the 
forehead or occiput may be expected to produce a burst- 
ing fracture crossing the coronal equator. Such a frac- 
ture is likely to occur in the temporo-parietal region, 
and nearer to the base than to the vertex. 4. Force 
applied to the vertex or base of the skull may be ex- 
pected to produce a fracture at the base.1 
Anatomical Peculiarities of the Skull. 
Having now briefly considered the elastic properties 
of the skull, let us next study its anatomical peculiari- 
ties, which, as I have already pointed out, may be ex- 
pected to modify the results which might be expected if 
the shape of the skull were regular and its thickness 
uniform. These peculiarities must be given due consid- 
eration if we would avoid the error of applying too 
rigorously the bursting theory ; at the same time, they 
must not be overestimated. This was the error of 
Felizet, who was right in attaching great importance to 
the architectonic conditions of the skull, but who was 
mistaken in supposing that his buttresses and centre of 
resistance would stand firm against all or most fractures. 
1 It may be worth while to call attention to the fact that there is no essential 
difference between a blow applied directly upon the vault or side of the skull 
and one transmitted through the spinal column by a fall upon the feet or but- 
tocks. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
37 
So Aran, before him, was right in supposing that 
fractures starting in one fossa of the sknll would often 
be limited to that fossa; but he erred in supposing this 
could be stated as a sfeneral law. Both of these theories 
depended upon what we may call the accidents of 
fractures of the skull; the essential, I believe-and the 
future may show that this view may be applied too 
rigorously-is to be found in the elastic properties of 
the skull, as revealed not only by the experiments of 
von Bruns and of his German followers, but also by 
those of Aran and of Felizet themselves, and by the 
investigations of others before their time, to whom allu- 
sion has already been made in the historical sketch 
at the beginning of this paper. 
The thinnest portions of the various bones of the skull 
are as follows: 
In the frontal bone. The walls of the frontal sinuses; 
the orbital plates; the temporal portions; and some- 
times on both sides of the crest for the attachment of 
the falx cerebri. 
In the ethmoid Lone. The horizontal plate. (The 
other parts of the bone may be regarded as outside of 
the true cranial case.) 
In the sphenoid bone. The orbital portion of the 
greater wings, and the walls of the sphenoidal sinuses. 
The basilar portion of this bone has a deceptive appear- 
ance of strength, on account of its thickness: but on 
section it will be seen to be of such open cancellated 
structure that it is not surprising to find that it is very 
often fractured. 
In the parietal bones. The lower border, just above 
the parieto-squamosal suture, and both of the inferior 
angles. 38 
MECHANISM OF INDIRECT FRACTURES OF TIIE SKULL. 
In the occipital hone. The floor of the cerebellar 
fossae; and, to a less extent, the floor of the posterior 
cerebral fossae. 
In the temporal hones. I take these bones last 
because they present some extremely interesting ana- 
tomical peculiarities, the importance of which I have 
not found dwelt upon as I think it ought to be. The 
thinness of the squamous plates is too familiar to need 
more than mention. But the temporal bone is also 
often very thin over the cotyloid depression for the head 
of the inferior maxilla. The mastoid portion is also 
sometimes occupied by such large open spaces as 
materially to weaken its walls. The petrous portion 
does not, on section, present everywhere that solid and 
rocky appearance to which it owes its name, and which 
it only partly deserves. The roof of the external audi- 
tory meatus is sometimes very thin, in a line parallel to 
and anterior to the superior ridge of the bone. The floor 
of this canal is also comparatively thin. The plate of 
vitreous which covers the anterior inclined plane of the 
bone is often a mere shell over the promontory above 
the superior semicircular canal, and further back, in 
front of the groove for the superior petrosal sinus, it 
overlies a mass of honeycombed cancellated tissue 
which communicates with the large cells of the mastoid 
process. These facts explain the many fractures which 
are found to run parallel to the crest of this bone, and 
which have often been wondered at. In like manner, 
the curious course which a fracture sometimes takes at 
right angles to the main axis of the petrous bone may 
be understood when we study the channels and excava- 
tions belonging to the middle and internal ear, the MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
39 
internal auditory meatus, the carotid canal, the groove 
for the inferior petrosal sinus, and the jugular foramen. 
These are some of the weak points of the bones of the 
skull. Others might be mentioned; as, for example, 
the antero-lateral rim of the foramen magnum, which, 
in some cases, is very porous, and far from so strong as 
its thickness would indicate. It will be noticed that 
all of these thin parts of the skull lie in or near the 
base, and clinical observation shows that they are very 
frequently the seat of fracture. 
There are a few other anatomical peculiarities of the 
skull to which I would like to call your attention before 
I leave a part of our subject which might well occupy 
much more time than we can spare it. First, in regard 
to the posterior clinoid processes. It was long a matter 
entirely unexplained that violence done to the skull was 
followed by no fracture, except one breaking off the pos- 
terior clinoid processes of the sphenoid bone. But the 
explanation is easy enough if we accept the " bursting 
theory," and recognize the fact that the tentorium cere- 
bell i is attached in front to these processes, and that 
when the long diameter of the skull is increased the 
tense tentorium holds back with an unyielding strain 
and tears these processes from their attachments to the 
rest of the bone. In this we have both a full explana- 
tion of the mechanism of these fractures and a beau- 
tiful confirmation of the " bursting theory " of indirect 
fractures of the skull. 
Again, let me call your attention to the peculiar con- 
ditions of the basi-sphenoid and petrous bones. These 
bones are never, I believe, united by bony union or 
close-fitting dentations, like the other bones of the 
skull. Their adjacent surfaces are simply applied 40 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
against each other and united by a membranous or 
ligamentous band. The plane in which these bones 
articulate is such that the basi-sphenoid is placed like a 
wedge between the apices of the two petrous bones. 
As a consequence, any force, like a blow on the vertex, 
driving the cranium down upon the spinal column, or a 
fall upon the buttocks or feet, driving the spinal column 
up against the cranium, will have the effect of forcing 
the wedge-shaped basi-sphenoid upward and forward 
between the two rigid petrous bones, with the frequent 
result of knocking off one or both of the apices of the 
latter. This form of fracture is another which has 
excited much surprise and some fanciful explanations; 
but, in the light of what has just been stated, it seems 
to me to be quite comprehensible. 
Finally, 1 have been struck by the fact that certain 
peculiar fractures of the base of the skull seem to have 
been due to support of a segment of the occipital bone 
furnished by the inclination upward and outward of the 
articular surfaces of the atlas, which embrace the con- 
dyles of the occipital bone and restrain it from rupture 
to such an extent that a fissure will pass on both sides 
of the protected region rather than through it. This 
form of fracture I illustrate by a beautiful specimen 
taken from the Mutter Museum of this College. 
Architectonic Peculiarities of the Skull. 
I cannot now do more than allude to the general oval 
shape of the skull, its various curves, arches, and but- 
tresses, the comparatively even shape and homogeneous 
character of the vault, and the irregular shape and vary- 
ing thickness and thinness of the base, with its promi- MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
41 
nences and depressions, its channels and its so-called 
sinuses. These are too complex to be detailed here, and 
too familiar to all to make this necessary. But I would 
call your attention to what Felizet has laid so much 
stress upon, the reinforcement of certain regions, as at 
the junction of the greater wings of the sphenoid bone 
with the frontal and temporal bones, and of the petrous 
portion of the temporal bones with the parietals; at the 
ridge for the attachment of the longitudinal and lateral 
sinuses within the skull and at those for the attachment 
of muscles at the back of the head, which vary in im- 
portance in different individuals. In addition, we may 
well bear in mind the comparative roundness of the 
vault and flatness of the base, and the wedge-like inser- 
tion of the lower borders of the parietal bones between 
the bevelled upper edges of the squamous bones, and 
the projection of the ends of the petrous bones against 
the basi-sphenoid, of which I have already spoken in de- 
tail. For most of the points one may consult the works 
on general and special anatomy, or, better still, the skull 
itself. They all must be considered in studying varia- 
tions from the result to be expected from the application 
of any given theory in regard to the mechanism of frac- 
tures of the skull, although, as I have said, they need 
not be expected to controvert any law of general appli- 
cability. 
Influence of the Soft Parts and Contents 
of the Skull. 
This is another portion of the study of fractures of 
the skull to which more time ought to be devoted than 
we can spare now. In a general way, it may be said 42 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
that the external and internal coverings of the skull- 
the dura mater and the pericranium, with the muscles, 
fascise, and skin-tend not only to deaden vibrations to 
such an extent that it is hard to know how to under- 
stand many expressions of those who have accepted 
what is known as the " vibration theory," but also to 
limit to a moderate extent the changes in shape which 
the skull may undergo, according to the "bursting 
theory." The action of the muscles must also be con- 
sidered of importance, as exemplified in such involun- 
tary and spasmodic contractions as prove sufficient of 
themselves to break other bones, and which may have 
more effect here than has yet been suspected. Let us 
imagine, for example, what might be the effect of a 
spasmodic contraction of the erector mass at the back 
of the head when a sudden blow comes upon the ante- 
rior part of the vertex, tending to flex the head. I wish 
it *were possible to go further into this inviting field of 
investigation. 
As to the contents of the skull, we have seen that 
Fabricius ab Aquapendente attributed fractures by coun- 
terstroke to the effort of the air, which he supposed the 
skull to contain, to escape from its cavity. We know 
better than this; but it does not seem needless to call 
attention to the fact that the skull is tilled with a much 
more incompressible material than air. In fact, the 
brain and its membranes, with the surrounding fluid, 
completely fill the skull with one of the most incom- 
pressible materials of which we have any knowledge. 
Under the influence of a blow, this material tends to 
increase the disruptive force, according to the well- 
known laws of hydrostatics. As a full cask may be 
burst by a blow, so there can be no doubt the skull may MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
43 
likewise be burst. The statements often made, which 
affirm or imply that the skull and its contents can be 
compared to a water-bed, are utterly erroneous. The 
fluid contained in the cranium, in a state of health, is 
far too little to justify any such comparison. Besides 
which, it is contained in a firm, unyielding case; while 
it is indispensable to a water-bed that its walls shall be 
soft and yielding. It has also' been intimated-and so 
able a man as Mr. Hilton thought he had demonstrated 
-that displacement of the cerebro-spinal fluid could be 
regarded as a protective against injury when the skull 
was struck. Mr. Hilton's experiment was not free from 
an important source of error, and one who studies care- 
fully the anatomical peculiarities of the cerebro-spinal 
axis must see, I think, that there is only one way for 
compensatory diminution in the contents of the skull to 
take place, namely, by displacement of its contained 
blood through its natural channels. This displacement 
can and does take place when time is afforded for the 
process, as in the case of a growing tumor; but the 
rapidity with which a blow tends to diminish the ca- 
pacity of the cranium far outstrips the speed with which 
the blood can escape; so that, as a matter of fact, the 
skull and its contents may be regarded as the very oppo- 
site of a water-bed, and more like a cask filled with fluid 
which may burst under a sudden increase of the pres- 
sure upon the inside of its walls. This fact is estab- 
lished not only by a correct knowledge of the physical 
conditions of the cerebro-spinal axis, but also by experi- 
ments and observations which I cannot stop to mention 
now. 44 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
Study of Cases. 
A great difficulty confronts at the outset one who 
tries to discover in how far the study of actual fractures 
of the skull will bear out any theory in regard to their 
mechanism which seems plausible. The difficulty de- 
pends upon the difference between the known factors 
in an experiment and the unknown factors in an acci- 
dent. It is often impossible, in the case of a fracture of 
the skull, to ascertain exactly the amount and direction 
of the force, the point to which it was applied, and the 
conditions of resistance or evasion of the whole cranial 
box. This consideration should lead to a modest and 
reserved fitting of what seem to be facts to any 
theory. Nevertheless, nothing can be learned by 
standing still; and we may, if not overconfident, make 
some advance in knowledge by testing a theory by an 
observation of what actually takes place. With this 
object in view, I have examined the published accounts 
of a very large number of cases of fracture of the skull, 
and I have collected more than a hundred (119) in 
which the details seem to me to be sufficient to warrant 
an approximative estimate as to the conditions under 
which the fracture occurred, and as to the results pro- 
duced. I cannot go over the records of these cases in 
detail, but I now show you drawings of all of the frac- 
tures, each accompanied by a reference to the source 
from which I have obtained it, and such verbal explana- 
tions as will, I trust, enable you to form some opinion 
as to the amount of support they can be credited with 
affording to the " bursting theory" which I have already 
described and endeavored to explain. In presenting MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
45 
these drawings to your attention, I must warn you 
against certain sources of error in them. The first 
depends upon the imperfection of the great majority-I 
might almost say of all-of the records from which they 
have been made up ; the second depends upon the great 
difficulty of representing upon a flat surface what may 
be gathered from a verbal description of so complex 
and intricate a thing as a fracture of the skull. 
In addition to the drawings representing each case of 
fracture by itself, I show you one in which I have trans- 
ferred to a single diagram all the fracture lines falling 
within the base of the skull. I do this to indicate, if it 
be possible, where fractures most frequently occur, and 
also to make clear the fact that the parts which Felizet 
has assumed to have peculiar strength-the petrous 
bones and the basilar portions of the occipital-seem, 
on the contrary, to be the very seats of election for frac- 
tures of the base. 
For convenience of comparison, I have arranged the 
drawings in classes according to the nature and direc- 
tion of the violence which produced them. Wherever 
there seemed to be doubt as to these points I have indi- 
cated this fact by a query mark (?). The direction of 
the violence is indicated, wherever this could be done, 
by an arrow pointing to the point of impact.1 
Class A1. Fractures caused by bloivs on the frontal region. 
Of this class I have only two cases. One caused by a kick from a 
horse above the right eyebrow, causing a direct fracture here, and an 
indirect meridional and oblique fracture of the parietal bone of the 
same side. The other case presents a fracture caused by a blow 
1 The plates published at the end of this paper have bepn prepared from those 
presented to the College, so that a single diagram may exhibit a number of 
fractures caused by the same sort of force. 46 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
with the handle of a pitchfork, high up on the frontal region. 
The fracture is in the base, is meridional, and passes from the 
right orbital plate through the sphenoid bone and the basilar pro- 
cess of the occipital, leaping across the foramen magnum, from the 
back edge of which start two converging fissures which meet in the 
cerebellar fossa on the left side, and end above the groove for the 
lateral sinus. 
Class A2. Fractures caused by falls upon the frontal region. 
Of these I have thirteen cases. Twelve present meridional fissures ; 
five of them being directly longitudinal, three of these passing directly 
through the whole basi-sphenoid bone. Seven are oblique; two of 
them bifurcated, and one passing through the whole basi-sphenoid 
bone; one passes from the point of impact to the lower part of the 
ridge for the straight sinus, after having passed across the middle 
of the petrous bone and encircled the foramen magnum. One shows 
a ring fracture, in addition to a meridional fracture from the frontal 
bone to the junction of the petrous with the basi-sphenoid. One 
is directly opposite to the point struck, is extensive and bifurcated. 
Class B1. Fractures caused by blows on the occipital region. 
Of these I have only two cases. One was caused by a spent ball 
striking the occiput to the left of the middle line, and shows an 
independent meridional fracture passing alongside of the internal 
ridge to near the foramen magnum, then crossing the petrous bone, 
dividing it transversely to its principal axis, and ending in the fora- 
men spinosum. The other case is a specimen from one of Perrin's 
experiments, in which the skull was thrown on a stone pavement 
covered with a layer of India-rubber. There is a separation of the 
coronal suture, and a prolongation of this as a bifurcated fissure in 
the right squamous bone. This specimen shows a division at right 
angles to the meridian, which may be due to an unusually weak union 
in the coronal suture, or to some peculiarity of the experiment. I 
have included this specimen among my drawings, because it is dia- 
metrically opposed to the bursting theory. But I think an experi- 
ment which involves throwing a skull detached from the body, can- 
not be considered very reliable in comparison with those in which 
the skull is fixed. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
47 
Class B2. Fractures caused by falls, striking upon the occipital 
region. Of these I have twenty-one cases. All show meridional 
fractures. Two of these pass directly through the crest for the 
lodgement of the straight sinus to the foramen magnum. One passes 
to the foramen magnum near this crest. Two pass through the 
whole of one side of the occipital bone, and one splits off' a piece of 
the parietal, and separates the lambdoid suture in part. One divides 
the frontal bone into halves. Six pass round the foramen magnum 
on one side, three dividing the petrous bone longitudinally and one 
transversely. One shows a longitudinal fracture passing across the 
foramen magnum and dividing the basi-sphenoid bone, as well as a 
partial ring-fracture. In two the fissure passes meridionally round 
the side of the head. One shows an independent fissure on each 
side, in the parietal bones. 
Class B3. Fractures due to blows on both the forehead and 
occiput. One such case I have found recorded by Herpin, in which 
there was a succession of bumps on each of these parts. The re- 
sulting fracture is a long fissure, passing longitudinally from the 
internal occipital protuberance to the foramen caecum, passing round 
the foramen magnum, very close to it, and dividing the whole of the 
basi-sphenoid: a beautiful meridional fissure. 
Class C1. Fractures caused by compression in a longitudinal 
direction: accidental. Hewett records two cases of this sort. In 
the first, a man fell on the back of his head, and a piece of timber 
fell on his forehead. The fissure is independent, and partly merid- 
ional. It divides longitudinally the middle of the horizontal plate 
of the ethmoid bone and the middle of the body of the sphenoid 
bone, passing then to the right through the greater wing of this 
bone, and bifurcating before passing in two fissures upon the squa- 
mous plate of the temporal bone. In the second, the history is far 
from clear, but it seems that the fracture was caused by the com- 
pression of a cartwheel passing across the forehead. The fracture 
is meridional and exactly like several in the next class. 
Class C2. Fractures caused by compression in a longitudinal 
direction: experimental. Of these I have nine cases. • Six show 
meridional fissures. One divides the skull from front to back over 
the vault. Three divide the skull to an equal extent through the 48 
MECHANISM OF INDIRECT FRACTURES OF TIIE SKULL. 
base, passing round the foramen magnum. In two there are two 
independent fissures. In one of these cases one of the two fissures 
is not meridional. Three of the cases show complicated fissures 
which may be due more to crushing than to bursting. 
Class D1. Fractures from blows on the parietal region. Of 
these I have only four cases. All show meridional fissures. Three 
pass straight down to the apex of the petrous bone, and one passes 
also up to the vertex. 
Class D2. Fractures caused by falls, striking on the parietal 
region. Of these I have fifteen cases, in all of which I think the 
fractures may be considered meridional. Four pass along the hori- 
zontal equator of the skull. Seven are transverse, three crossing 
the base from side to side, two going half way across, one involving 
only the ends of the petrous bone, and one passing across the vault 
at the back part of the parietal bones, and then passing forward to 
the base. Four are diagonal, two of them passing across the sella 
turcica. 
Class E1. Fractures caused by compression in a transverse 
direction : accidental. Of these I have five cases. In all, the frac- 
tures are transverse and meridional. Two pass across the basi- 
sphenoid bone and upward on both squamous bones. In one both 
parietal bones are split independently, the fissures passing down 
through the petrous bone. In one the coronal suture was separated, 
and a piece broken out of each parietal, beside an independent frac- 
ture of the occipital and petrous bones at the base on one side. 
Class E2. Fractures caused by compression in a transverse 
direction: experimental. Of these I have five cases. In all, the 
fissures are transverse and meridional. In four the basi-sphenoid is 
divided transversely, and in three the fissure involves also the tem- 
poral bones. In one case the coronal suture is disarticulated. 
Class F. Fractures caused by falls, striking on the temporo- 
frontal region. Of these I have only two cases. In one the 
fracture is meridional; in the other it is equatorial, and seems to 
illustrate the shoving of the posterior half of the skull over the 
anterior half by the impact of the spinal column on the base in an 
oblique direction. MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
49 
Class G. Fractures caused by compression in a diagonal direc- 
tion : experimental. Of these I have five cases. In four the fissures 
are meridional, two being quite complicated. In one case there is a 
separation of the posterior inferior angle of the parietal bone, and the 
dorsum of the sella turcica is broken off. 
Class II1. Fractures caused by blows on the vertex: accidental. 
Of these I have six cases. In all, the fractures are meridional; in 
five they are transverse and in one longitudinal. 
Class II2. Fractures caused by blows on the vertex: experimental. 
Of these I have three cases. All of them show beautiful meridional 
fissures, one transverse and two longitudinal, one of the latter divid- 
ing the skull completely into halves. 
Class H3. Fractures caused by falls upon the vertex: acci- 
dental. Of these I have seventeen cases. In all, the fissures are 
meridional and can, I think, be attributed to a burst. In one the 
front half of the skull is divided longitudinally, and in one the pos- 
terior half is similarly divided. In one the fissure divides the 
skull into halves longitudinally; in two it divides it into halves trans- 
versely. In one the basilar artery was found caught in a transverse 
fissure of the basilar process of the occipital bone. 
Class J1. Fractures caused by falls upon the condyles {trans- 
mitted from feet) : accidental. Of these I have only three cases. In 
two both posterior clinoid processes were broken off-which can be 
attributed to the lengthening of the antero-posterior diameter of the 
skull-and there was a transverse fracture of the apex of the petrous 
bone. In the third case there is only a longitudinal fissure of the 
horizontal plate of the ethmoid bone on one side. 
Class J2. Fractures caused by blows on the condyles: experi- 
mental. Of these I have four cases. In all of them the dorsum of the 
sella turcica has been torn off by the elongation of the antero-pos- 
terior diameter of the skull. In two cases this is the only fracture. 
In one case the whole base is also divided transversely, the fissure 
passing across the basilar process of the occipital bone. In one case 
there are also three independent fissures, all transverse. 50 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
CONCLUSIOX. 
The analysis of these 119 cases shows that 111 pre- 
sent fissures which correspond to what might be expected 
from an application of the principles of the " bursting 
theory," and only 8 seem to contradict it. This result, 
which has surprised me by its apparent completeness, 
seems to establish this theory by the best test which we 
can apply to it, so that it appears to rest upon a very firm 
tripod of reasoning, experiment, and clinical observation. 
I trust it will not be supposed that, in making so 
much of the bursting theory in this paper, I have over- 
looked the fact that there are fractures which cannot be 
accounted for by it. There are some fractures in which 
the force applied is so great, and acts in such a manner, 
that the skull is crushed so as to hide any evidence of 
the play of its elastic properties, the fracture being of a 
comminuted sort; and there are others in which, as I 
have noted in passing, one segment of the skull seems 
to be shoved over the other by forces of pressure and 
counter-pressure which require some study before their 
mode of operation can be understood. In this connec- 
tion it is of importance to learn in any case the position 
which the skull has held in relation to the spinal column, 
or to any body capable of exerting counter-pressure. 
No less is it important not to overlook the counter- 
pressure which is caused by the simple vis inertice, of the 
skull, and its contents. 
But it would be impossible to speak of all the influ- 
ences which may modify the strict application of any 
one theory in regard to fractures of the skull. I have 
laid before you all the evidence which I now can in re- MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
51 
gard to this matter; and I must close with the expres- 
sion of my own conviction that the supreme law gov- 
erning the production of indirect fractures, is that which 
depends upon the fact that the skull is practically a 
hollow elastic case, approximately oval in shape, and 
which may be briefly formulated as follows: When a 
sufficient force is applied to any curvilinear part of the 
skull, if this part do not give way immediately, the axis 
of the skull lying in the same line as that of the applied 
force is shortened; all the axes lying in planes at right 
angles to this line are correspondingly lengthened, with 
a proportional lengthening of their circumferences, and 
separation of their meridians ; so that the direct depress- 
ing force is converted into an indirect disruptive force 
actino; at ri^ht angles to the direction of the former. 
The effect is to produce a fissure, or fissures, which will 
have a general meridional direction. 
The application of this law is subject to certain modi- 
fications due to the anatomical and architectonic peculi- 
arities of the skull, its coverings and contents, and to 
certain exceptions due to the amount and velocity of the 
force applied as well as to the coming into play of peculiar 
counter-forces. 52 
MECHANISM OF INDIRECT FRACTURES OF THE SKULL. 
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Winslow. Traitd de la tete. (Louis: Receuil, pp. 157, 158.) PLATE I. 
Independent, meridional fissure caused by kick by a horse; 
skull broken in above orbit. 
PLATE II. 
Fissures caused by force applied to forehead; by falls. PLATE III. 
Fissures caused by force applied to forehead in an oblique direction ; by falls. 
No. 11 continued up over frontal bone to beyond coronal suture on left side. 
PLATE IV. 
Fissure caused by force applied to occiput; blow by a spent ball. PLATE V. 
Fissures caused by force applied to occiput; by falls. 
No. 25 continued to apex of petrous bone, through anterior inclined plane. 
Nos. 33, 97, and 99, were on right side of skull. (See also Plate VI.) 
PLATE VI. 
Fissures caused by force applied to the occiput; by falls. 
No. 97 passed up on right to lambdoidal suture. 
No. 98 passed up on left to lambdoidal suture. 
No. 99 passed up in front of lambdoidal to near sagittal suture. 
No. 25 passed round left side to root of zygoma. (See also Plate V.) PLATE VII. 
Fissures caused by force applied to occiput; by falls. 
One fissure (No. 35) caused by force applied to occiput and forehead 
alternately. 
PLATE VIII. 
Fissures caused by compression in fronto-occipital diameter. 
Nos. 36 and 37, accidental. 
Nos. 39, 40, 41, and 43, experimental. 
No. 37 passed up and forward on right parietal bone to near its middle. 
No. 43, fissure in cerebellar fossa involved vitreous table alone. PLATE IX. 
Fissures caused by compression in occipito-frontal diameter; experimental. 
No. 47 was on left side of skull. 
PLATE X. 
Fissures caused by blows on side of head. 
No. 51 passed up to sagittal suture. PLATE XI. 
Fissures caused by falls, striking on parietal boss. 
PLATE XII. 
Fissures caused by falls, striking on side of head. 
No. 62, fracture at back of skull passed over vault through both parietal bones, 
caused by fall on left parietal boss. PLATE XIII. 
Fissures caused by compression in transverse diameter; accidental. 
No. 69, extension of fissure into side of base imperfectly described. 
No. 70, fissure on each side continued upward in coronal direction half way 
to sagittal suture. (See also Plate XIV.) 
No. 71, principal fissure was in coronal suture ; the fracture at base hard to 
distinguish, as patient survived forty years. (See also Plate XIV.) 
PLATE XTV. 
Fissures caused by compression in transverse diameter. 
(See also Plate XIII.) PLATE XV. 
Fissures caused by compression in transverse diameter; experimental. 
PLATE XVI. 
Fissure caused by compression in transverse diameter ; experimental. 
No. 76, separation of coronal suture. PLATE XVII. 
Fissures caused by compression in diagonal direction ; experimental. 
PLATE XVIII. 
Fissures caused by compression in diagonal diameter; experimental. PLATE XIX. 
Fissure caused by blows on top of head ; accidental. 
No. 85. See also Plate XX. 
Nos. 86 and 87 passed across whole of vault and into base on both sides. (See 
also Plate XX.) 
No. 88, fissure passed to carotid canal ; end of petrous bone also broken off". 
Child, four years old. Billet of wood fell considerable distance, struck 
on forehead. (See also Plate XX.) 
No. 89, man struck on " crown of head " by a piece of iron falling a consid- 
able distance. 
PLATE XX. 
Fissures caused by blows on top of head ; accidental. 
No. 85, fissure passed up to near sagittal suture. (See Plate XIX.) 
No. 86, fissure completely bisected vault. (See Plate XIX.) 
No. 87, vault crushed in and fissure connected with those in base. (See Plate 
XIX.) 
No. 88, fissure extended up to centre of left frontal bone. (See Plate XIX.) PLATE XXI. 
Fissures caused by blows on top of head ; experimental. 
No. 91 passed to foramen magnum to left of median line. Placed on right 
side here for convenience. 
No. 92 divided base from front to back, splitting basi-sphenoid. 
PLATE XXII. 
Fissures caused by falls on top of head; accidental. 
No. 94 divided skull into halves longitudinally. (See Plate XXIII.) 
No. 95 passed to sella turcica. (See Plate XXIII.) 
No. 96 passed to foramen magnum. (See Plate XXIII.) 
No. 100 passed to foramen magnum. (See also Plate XXIII.) 
No. 106 divided skull into halves. (See Plate XXIV.) 
Nos. 107 and 108 were on left side. (See Plate XXIV.) 
No. 109, fissure passed to foramen magnum. (See Plate XXIV.) 
No. 110 fissure passed to jugular foramen. (See Plate XXIV.) PLATE XXIII. 
Fissures caused by falls on top of head; accidental. 
No. 94, fissure divided skull into halves longitudinally. (See Plate XXII.) 
Nos. 95, 96. See also Plate XXII. 
No. 100 passed upto apex of lambdoidal suture and through sagittal to frontal 
bone. (See also Plate XXII.) 
PLATE XXIV. 
Fissures caused by falls on top of head ; accidental. 
Nos. 105 and 106 divided skull into halves. (See Plate XXII.) 
No. 107 passed up on left side to middle of parietal bone. (See Plate XXII.) 
Nos. 108, 109, 110 passed up to near vertex. (See Plate XXII.) PLATE XXV. 
Fissures caused by falls on feet; accidental. 
PLATE XXVI. 
Fissures caused by blows on condyles ; direct or transmitted ; experimental. PLATE XXVII. 
Lines of fissures in 100 cases. It has been impossible to represent all that 
passed through the basi-sphenoid, either longitudinally or transversely, or those 
which passed along the anterior inclined plane of the petrous bone.