THE EXTENT OF THE VISUAL CORTEX IN MAN, 
AS DEDUCED FROM THE STUDY OF LAURA 
BRIDGMAN’S BRAIN. 
HENRY H. DONALDSON, Ph. D., 
Assistant Professor of Neurology at Clark Univer- 
sity, Worcester, Mass. 
Reprinted from The American Journal of Psychology, Vol. IV, 
No. 4, August, 1892. THE EXTENT OF THE OF THE COR- 
TEX IN MAN, AS DEDUCED FROM THE STUDY 
OF LAURA BRIDGMAN’S BRAIN. 
Henry H. Donaldson, Ph. D., 
Assistant Professor of Neurology in Clark University, Worcester, Mass. 
Some peculiarities of the cerebral cortex, in the case of 
Laura Bridgman, have already been described in this Jour- 
nal (I>2). 
It was there pointed out that the three localities examined 
within the occipital lobe had the cortex thinner in the right 
hemisphere. The optic nerve and tract belonging to the left 
eye were the thinner, and in the right cuneus, the gyri were 
irregular. These facts all pointed to a greater disturbance 
affecting the right occipital lobe. Since in the left eye vision 
was completely lost at the age of two years, while it persisted 
up to the eighth year in the right, the thinness of the cortex 
on the right side was explained by the earlier loss of vision 
in the left eye, a lesion which was assumed to have arrested 
its development. Since the completion of the papers men- 
tioned above, a further consideration of the case suggested 
that this brain might be used to determine the extent of the 
visual area in man. In following out this suggestion it has 
been assumed: (1) That the thinning of the cortex was 
due to an arrest of development; (2) that this thinning 
would extend over the entire visual area; (3) that, in the 
regions compared, the disturbance in vision was the principal 
influence acting to arrest unequally the growth of the cortex ; 2 
DONALDSON ; 
(4) that the cortex would be most thinned upon the side of 
the brain opposite to the eye and nerve most affected; (5) 
that the visual area in the normal brain gradually merges 
into the surrounding areas, and that hence the cortex on the 
outer limits of this area would, in this case, be but slightly 
different on the two sides. 
The observations on which my conclusions are based were 
made in the following manner : 
On a model of the brain, a boundary line was marked off 
as follows: Beginning at the mantle-edge on the dorsal sur- 
face the boundary passed laterad from the mesal end of the 
sulcus lying next caudad to the superior retrocentral sulcus, 
to the dorsal end qf the ascending ramus of the first temporal 
sulcus, following this ventrad to its junction with the first 
temporal sulcus, and thence took the shortest path over the 
lateral and ventral surfaces, to the most cephalic end of the 
calcarine fissure, and there passed dorsad to join 
the mantle-edge at the point of departure. There was thus 
cut off a pyramidal portion of the hemisphere, with the plane 
of its base determined by this boundary, and having the 
occipital pole for its apex. 
For the purpose of comparison, this surface was first 
divided into six areas, and ultimately, by subdivision, into 
ten areas. The following is a description of the areas. 
I. The superior-parietal area. Bounded mesad by the 
mantle-edge, laterad by the interparietal sulcus, cephalad by 
the sulcus next caudad to the superior retrocentral sulcus, 
caudad by the anterior occipital sulcus. 
I. was subdivided into a cephalic portion, I. (a), lying 
cephalad to the cephalic stipe of the interparietal sulcus, and 
a caudal portion, I. (b), lying caudad to the same. 
11. The area of the angular gyrus. Bounded mesad by 
the interparietal sulcus, laterad by an arbitrary line uniting 
the junction of the first temporal and its ascending ramus to 
the transverse occipital sulcus, cephalad by the ascending 
ramus of the first temporal sulcus, and caudad by the anterior 
occipital sulcus. 
11. was subdivided into a cephalic portion, 11. (a), lying 
cephalad to the ascending ramus of the second temporal sul- 
cus and a caudal portion, 11. (b), lying caudad to the same. 
111. Area of the cuneus. Bounded dorso-cephalad by the 
parieto-occipital sulcus, ventrad by the calcarine fissure, and 
caudad by the mantle-edge. 
IV. The area of the occipital pole. Bounded mesad by 
the mantle-edge which separates it from the cuneus, laterad 
and cephalad by the anterior occipital sulcus, caudad by the VISUAL CORTEX. 
3 
lateral occipital sulcus, and an arbitrary line joining the 
mesal end of the latter with the calcarine fissure. 
IY. was subdivided into a lateral portion, IV. (a), lying 
laterad to a secondary sulcus which runs through the middle 
of this area, parallel to the mantle-edge, and a mesal portion, 
IY. (b), lying mesad to the same. 
Y. The praecuneal area. This includes that part of the 
praecuneus which lies cephalad to the parieto-occipital sulcus, 
and caudad to the boundary line. 
YI. The ventral area. Bounded mesad by the calcarine 
fissure, laterad and caudad by the lateral occipital sulcus and 
its arbitrary continuation to the junction of the first temporal 
sulcus with its ascending ramus, cephalad by the base line. 
YI. was subdivided into a mesal portion, YI. (a), lying 
between the calcarine fissure and the fourth temporal sulcus, 
including, however, only the dorsal two-thirds of the gyrus 
lingualis, and a lateral portion, YI. (b), lying laterad to 
YI. (a). 
The brain itself was now compared with the model. The 
portion corresponding to each one of the ten areas just enumer- 
ated was cut into a number of blocks, and the position of each 
block was carefully marked on the model. The block was 
then mounted and the thickness of the cortex determined. 
There were sixty-two such blocks for each hemisphere. 
The thickness of the cortex was determined in the follow- 
ing manner: The block was imbeded in celloidin and cut 
into sections about .05 mm. thick, stained with van Gieson’s 
Picro-Fuchsin and mounted in the usual way. 
By this stain the gray matter was colored a much deeper 
red than the white and thus well differentiated from it. The 
thickness of the cortical layer was measured with an eye- 
piece micrometer, each division of which had the value of 
.067 mm. 
The following is the detail of the method of measurement: 
By means of a camera lucida each specimen was drawn on a 
card, being enlarged about six diameters. The actual length 
of the cortex in each specimen was next obtained by direct 
measurement. The thickness of the cortex was measured at 
the bottoms and sides of the sulci and at the summits of the 
gyri. Whenever any of these localities was sufficiently ex- 
tended, more than one measurement was taken. In general 
the measurements of the thickness of the cortex were made 
at intervals of 5 mm. 
Bach measurement was then recorded at the corresponding 
point on the drawing of the specimen, and by this means any 
observation could be easily verified. 4 
DONALDSON; 
The above was all done by my assistant who was not in- 
formed of the purpose of the investigation. 
The next step was to cover all the labels, both on the speci- 
mens and the drawings. The drawings were then shuffled and 
the specimens arranged in the final order in which the draw- 
ings stood. In this way the specimens from the right and 
left sides were mixed together and all order among them 
destroyed. All the measurements were then repeated by 
myself. The figures thus obtained were final and have not 
been altered. 
As a result there was obtained for each section a length of 
cortex and a certain number of measurements giving the 
thickness of the cortex at about equal intervals of 5 mm. 
The average of the measurement for thickness multiplied into 
the length represented the area of the cross-section of the 
cortex in the given block. In order, however, to compare 
these areas with one another, it was necessary that the length 
of cortex should be the same on both sides. As this was 
rarely, if ever actually the case, the adjustment was made by 
always choosing as a norm the length of that side where 
the cortex was shortest. lu comparing symmetrical points 
the difference in the area is thus rendered dependent upon 
the average thickness of the cortex alone. 
In making up the tables from these observations it has to be 
kept in mind that if from one block in a certain area we have 
five or ten times the length of cortex that is obtained from its 
neighbor, that then the average derived from the measure- 
ments of this longer cortex applies to five or ten times as 
much of the region from which it is taken and hence should 
enter into the sum from which the average is derived five or 
ten times to its neighbor’s once. In making the tables, 
therefore, the average thickness of the cortex for each block 
is multiplied by the length of cortex to which it applies. 
The areas thus obtained are added together and the sum 
divided by the number representing the sum of the several 
lengths of cortex. The quotient represents the average thick- 
ness of the cortex for the area in question, the thickness as 
determined for each block having thus been allowed its pro- 
portionate weight. Since the length of the cortex was very 
different in the different blocks the length in that block 
which had the shortest cortex was taken as a standard. The 
minimal length was just 5 mm. This length of 5 was taken 
as a unit, and all the other lengths have been written in 
the tables as multiples of this unit. In other words those 
numbers represent the true length of the cortex divided by 5. 
Since the reduced lengths enter as factors into the columns in 
which the areas are given, the figures there also represent VISUAL CORTEX, 
5 
the true areas divided by 5. With this explanation we pre- 
sent the first table. 
Table I. 
To show the average thickness of the cortex in the several subdi- 
visions, with the absolute difference between the two sides and thickness 
of right side in percent. 
Area. 
No. 
Number of Blocks. 
Length of Cortex 
divided by 5. 
Area of Cortex 
in section, 
divided by 5. 
Average 
thickness 
in mm. 
Left sid 
ai 
Abso- 
lute dif- 
ference 
in mm. 
e stand- 
[•d. 
Percen- 
tage 
thick- 
ness of 
the 
right 
side. 
Name. 
Left. 
Right. 
Left. 
R’h’t 
Superior parietal. 
I. a. 
2 
9.1 
24.68 
24.49 
2.71 
2.69 
+.02 
99.2 
excluded. 
Superior parietal. 
r. b. 
3 
12.5 
37.27 
34.32 
2-98 
2.74 
+.24 
91.9 
Angular gyrus. 
II. a. 
5 
20.5 
58.09 
56.97 
2-83 
2.78 
+.05 
98.2 
Angular gyrus. 
II. b. 
6 
20.2 
61.15 
53.30 
3-02 
2.63 
+.39 
87.0 
Cuneus. 
III. 
11 
38.7 
82.69 
79.13 
2-13 
2.04 
+.09 
95.7 
Occipital pole. 
IV. a. 
6 
19.1 
42.79 
41.83 
2 24 2.19 
+.05 
97.7 
Occipital pole. 
IV. b. 
3 
14.8 
32.76 
31.93 
2-21' 2.15 
+.06 
97.2 
Praecuneus. 
V. 
4 
19.6 
53.56 
58.97 
2.73 3-00 
—.27 
109.8 
excluded. 
Meso-Yentral. 
VI. a. 
6 
16.4 
37.50 
33.41 
2.28 2.03 
+.25 
89.0 
Ventral. 
VI. b. 
17 
60.1 
140.82 
148.37 
2.34 2-46 
1 
—.12 
105.1 
excluded. 
Explanation of Table I, 
In this table are entered the numbers for the ten subdivis- 
ions. The numbers for the larger areas, e.g. 1., etc., are not 
entered because in the presence of the subdivisions they are 
superfluous. They can, moreover, be obtained in any case 
by summing the numbers given for the component subdi- 
visions. 
Taking the columns of the table from left to right we have 
the following data: 
(1) Hame of area, (2) numerical designation of the subdi- 
vision, (3) the number of blocks cut from the subdivision, 
(4) the total length of the cortex in said blocks, divided by 5, 
as previously explained. This length has been adjusted so 6 
DONALDSON : 
that it is equal on both sides of the brain. The product of 
this last number into the number representing the average 
thickness of the cortex in this subdivision, first for the (5) 
left, then for the (6) right side. The number in millimeters, 
representing the average thickness of the cortex in the given 
subdivision, first for the (7) left, then for the (8) right side. 
The larger number of each pair in these two columns is 
printed in heavy faced type. (9) The absolute difference in 
millimeters between the pairs of figures in the last two col- 
umns, showing by how much the number for the left side ex- 
ceeds that for the right. (10) The thickness of the right 
side expressed as a percentage. The thickness of the left 
side being taken as a standard i. e., equal to 100%. (11) 
Finally, “excluded” is put after each subdivision which can 
not be considered as part of the visual area. 
The numbers for each subdivision as entered in Table I. 
have been derived from detail tables, giving the length of 
cortex and average thickness of the same for each block be- 
longing to the subdivision. These detail tables would be 
worth publishing only in case they were accompanied by fig- 
ures showing exactly the point at which each section was 
taken. At present that is not practicable, hence they are not 
given. 
An examination of Table I. shows that in two subdivisions 
the cortex on the right side is thicker than on the left. Since 
we are determining the extent of only that cortex on the 
right side which is thinner, these two cases, Y. and YI. (b), 
are to be at once excluded. In the remaining eight cases 
the thickness of the right side is from 99.2% to 87.0% of 
that of the left. The next question, therefore, is what differ- 
ence may be considered significant for our purpose. 
To this end we must determine first, what variations occur 
in the thickness of the two sides of normal brains. 
I have determined the relative thickness of the occipital 
cortex in the brains of six males and three females, sampling 
each hemisphere at three points (2,p-62'). 
Conti(3) has determined the same for seven males and four 
females. The figures apply to his post-rolandic region, 
namely all that which lies behind a vertical plain passing 
through the mesal end of the rolandic fissure. 
Franceschi’s(4) observations were made on ten male and 
ten female brains and appear to apply to the occipital lobe of 
Ecker. 
In general, then, the figures obtained by Conti and Fran- 
ceschi are comparable with those which I have obtained from 
these last measurements of the Bridgman brain. The avera- 
ges from the controls measured by myself are taken from VISUAL CORTEX. 
7 
three localities only, and may, therefore, be expected to show 
greater variations than the figures of the Italian observers. 
The following, Table 11., shows the thickness of the cortex in 
the left and right occipital lobes of the normal brain, giving 
the thickness of the right side as a percentage of that for the 
left. 
Table 11. 
t 
Males. 
Females. 
Average thick- 
ness of Cortex 
in mm. 
Average thick- 
ness of Cortex 
in mm. 
Authority. 
Date 
Locality exam- 
ined. 
| No. of Brains- 
Left. 
Right. 
Percentage 
thickness of 
right side. 
| No. of Brains. 
Left. 
Right. 
Percentage 
thickness of 
right side. 
Conti. 
1884 
Pest Eelandic 
Region. 
7 
2.08 
2.06 
99.0 
4 
2.03 
2.03 
100.0 
Franceschi. 
1886 
Occipital Lobe. 
10 
2.28 
2.29 
100.4 
10 
2.16 
2.14 
99.0 
Donaldson. 
1891 
Three points in 
Occipital Lobe; 
6 
2.65 
2.62 
98.8 
3 
2.48 
2.54 
102.4 
Average, 99.5 
Average, 99.8 
Table 11. shows the greatest difference between the right 
and left sides in the case of the six normal males ex- 
amined by myself, the right side being the thinner, 98.8% 
of the left. In the females the right side is less thin, averag- 
ing for the seventeen cases 99.8%, while for the twenty-three 
males it is 99.5%. 
Taking the greatest difference found, 98.8%, and applying 
it to Table I. we exclude area I. (a), since there the right 
side differs from the left less than in the case of the normal 
males Just cited. 
The other differences shown in Table I. we may now re- 
gard as significant and employ them for plotting the visual 
area. See Plate I. 
According to these figures the outline of the visual area is 
the following: Commencing where the cephalic stipe of the 
interparietal sulcus cuts the mantle-edge and passing latero- 
eephalad along the latter to its junction with the inferior 
retrocentral sulcus, the boundary then takes the shortest line 8 
DONALDSON : 
to the ascending ramus of the first temporal sulcus, following 
this to its union with the sulcus, from here the shortest line 
to the lateral occipital sulcus from the mesal end of which an 
arbitrary line turns toward the fourth temporal sulcus, 
running parallel to this sulcus it cuts the gyrus lingualis so 
as to leave the ventral third of the latter in connection with 
the fourth temporal sulcus and continues to a point just ven- 
trad of the cephalic end of the calcarine fissure, which it joins 
by an arbitrary line running dorsad, it then passes caudad 
along the calcarine fissure to the junction of the same with 
the parieto-occipital sulcus, and finally along this sulcus to 
the mantle-edge, then eephalad along the latter to the point of 
departure. 
Such are the limits of visual area, as determined by this 
method, in the right hemisphere of the Bridgman brain. 
All previous direct determinations of this area in man have 
been by the method of limited lesions, and I find that my out- 
line follows so closely that given by Gowers(5) in his diagram 
and obtained by the latter method, that I venture to think 
that the two methods lead to almost identical results and 
hence mutually support one another. 
The visual area here outlined can, however, be examined 
in detail with advantage. The areas of the cuneus and that 
of the occipital pole [III., IV. (a) and IV. (b)] show the 
cortex on the right side only slightly thinner than on the left. 
The areas immediately around those just mentioned, viz., 
I. (b), 11. (b) and VI. (a), show the greatest thinning on the 
right side. Beyond this second series we have but one other 
area, 11. (a), in which the difference is again small. 
The theoretical explanation for this relation of things is the 
following: The cuneus and the occipital pole form the more 
fundamental portion of the visual area, hence would be earlier 
developed and more resistant to disturbing influences. If 
such were the case the differential effect of the lesion would 
be less evident in this region because the growth was more 
nearly complete at the date of the injury. Moreover, both 
eyes are represented on each side in the areas of the cuneus 
and occipital pole, and hence the loss of sight in the left eye 
would have produced some arrest on the left side, though we 
should expect the arrest to be decidedly less than on the 
right. So much by way of explaining why the regions of the 
cuneus and occipital pole do not show greater differences in 
the two sides. 
To explain why the surrounding region does show greater 
differences, I assume, first, that this region reaches complete 
development later, and would, therefore, be more affected un- 
der these conditions. Where the greatest difference occurs, VISUAL COUTEX. 
9 
namely, in the caudal portion of the angular gyrus, 11. (b). 
We have a region which is held by some authors to be in con- 
nection with the opposite eye mainly, and hence we have here 
two conditions which would induce the greatest difference in 
growth between the two sides. In the outermost area, 
11. (a), I look upon the visual representations as decreasing, 
hence the loss of vision would produce a less evident arrest 
here. 
It is hardly desirable to further dwell on these explanations, 
since, in part at least, they can be tested, and it can thus be 
determined whether they are valuable. 
In this connection there is one remaining observation to be 
noted. The mounted specimens of the cortex all show to the 
naked eye a clear stratification due to a light line. If the 
specimens are sorted according to the distinctness of the light 
line, disregarding the labels, and we put by themselves those 
in which the line is clear and sharp, it is found that we have 
all the samples of the cortex from the cuneus, the occipital 
pole, and also from the affected part of the gyrus lingualis. 
It thus happens that the line of Baillarger or of Gennari, as 
it has been rechristened by Obersteiner, is co-extensive in 
this brain with portions of the visual area, which I have 
called fundamental, but also runs over to the gyrus lingualis, 
which can not be included in that part for the reasons above 
given. So evident a structural peculiarity must have some 
physiological significance, but this case as it stands, does not 
show what that is. 
We conclude then that in this single brain we have the 
entire visual area marked out. This area includes the cuneus 
and angular gyrus, but does not pass onto the ventral surface. 
The thinning of the cortex is not the same throughout the 
visual area, but is small in the cuneus and occipital pole, 
large in the areas immediately surrounding it, and, finally, 
small again in the most outlying portions. The explanation 
which I have offered for this, is the stage of development in 
which the various portions of the cortex were found at the 
time vision was lost, and the degree to which each eye is rep- 
resented in several portions of both areas. Finally, Gennari7s 
line almost coincides with the fundamental portions of the 
areas, but oversteps it so far as to take in the dorsal portions 
of the gyrus lingualis, and thus, at present, cannot be ex- 
plained as a peculiar character of the fundamental portion. 
The idea involved in this investigation is not novel. The 
observations of Huguenin(6), Burckhardt(7), Mickle(8) and 
Mills(9) were based upon it, but this, I think, is the first 
time that advantage has been taken of an opportunity to ap- 
ply it in detail. 10 
DONALDSON ; 
To myself the point of most interest is that, if these conclu- 
sions are warranted, we have now, through the early destruc- 
tion of sense-organs and the subsequent examination of the 
cortex, a means of experimentally determining in animals the 
limits of the several sensory areas. For the feasibility of this 
plan, the experiments of v. Gudden and his school already 
offer some indirect support. 
Explanation of Plate I. 
This plate has been made in the following way: On the 
right side the caudal portion of the right hemisphere is repre- 
sented in some detail. There are three views: Fig. 1, 
lateral; Fig. 2, caudal; Fig. 3, mesal. The reversed out- 
line of this same portion is represented on the left side of the 
plate. The boundary of the portion taken is marked by a 
heavy line. On the left side the limits of the subdivisions 
are all marked by broken lines, and within each subdivision 
is given its numerical designation and the average thickness 
of the cortex, in millimeters. These are repeated on the 
right side, but the broken lines are omitted. As will be seen, 
in certain cases, some of these data are omitted. No ventral 
view is given because the cortex there is excluded. The ex- 
cluded portions, so far as shown, are left white, but on the 
right side the less affected subdivisions are hatched with a 
single line, while the more affected are so indicated by a 
doubly hatched line. The hatched portion on the right side, 
therefore, represents the visual area as determined. 
Bibliography. 
Reference rw™ 
Number. Date' 
Title, 
1. 1890. Donaldson, H. H. Anatomical observations on the 
brain and several sense-organs of the blind deaf-mute, 
Laura Dewey Bridgman. American Journal of Psy- 
chology, Vol. 111, No. 3. 
2. 1891. Ibid. American Journal of Psychology, Vol. IV, 
No. 2. 
3. 1884, Conti, A. Dello spessore, della corteccia cerebrale 
nell’ uomo. Torino. Giornnle della P. Academ. di Medic- 
ina. Torino. Fasc. 11-12 Nov., Dec., 1884. (Full ta- 
bles. 
4. 1886. Franceschi. Sulla varia grossezza della sostanza 
grigia degli emisferi cerebrale e del centri psico-motori 
dell’ uomo. Bologna. Bull, d sc. Med. di Bologna, 
1886. 6s. XVIII, pp. 153. (Tables.) 
5. 1888. Gowers, W. R. A manual of diseases of the nervous 
system. Vol. 11. London, 1888. Vide p. 19. Plate I. 
Showing three aspects of the occipital lobe 
Fig. 1. Lateral aspect. 
Fig. 2. Caudal aspect. 
Fig. 3. Mesal aspect. VISUAL COETBX. 
11 
6. 1878 
Huguenin. Em Beitrag zur Physiologic der Gross- 
hirnrinde. Correspondenzhlatt f. Schweizer Aerzte. 1878. 
Nr. 22. 
7. 1879 
Burckhardt. Atrophic des Gyrus Angular is nach 
Yerlust eines Augcs. Eericht pro 1879 iiber die 
Berner Canton Austalt, Waldau. (Abstract in Central- 
blatt f. Nervenhielkunde, etc. 1880, p. 361.) 
8. 1892 
Mickle, W. J. Localization of the visual centres of 
the cerebral cortex. Med. Times and Gazette. 1882, 
Jan. 28. 
9. 1889 
Mills, C. K. Brain specimens chiefly illustrating 
localization. University Med. Magazine, November, 
1889. (Philadelphia.)