ON THE BRAIN OF ATELES PANISCUS 497 
inwards; and, besides its general curvature, it has a secondary 
inflexion, so as to be a little sinuous. It is wide at its commencement, 
but rapidly narrows, until, where it bends inwards, its walls are so 
close together as to give it the appearance of a mere fissure, whose 
sides are apt to adhere together in such a manner as seriously to 
interfere with the satisfactory definition of the posterior limits of the 
cornu. In preparing the specimen, of which fig. 5 is a representation, 
for the artist, I therefore took care not to extend these limits. 
artificially, rather preferring to leave a portion of the cornu unopened 
than to exaggerate its length. 
In the other brain I found the posterior cornu, on the right side 
(dissected in the ordinary manner), to be traceable, without the least 
difficulty, to within a very short distance of the posterior limit of the 
hemisphere ; while in the left hemisphere, which I examined by 
making successive vertical sections from behind forwards, the 
posterior cornu ended at fully a quarter of an inch distance from the 
posterior extremity of the hemisphere. Such sections are of 
particular value ; for they show the extent of the cornu without any 
disturbance of its natural dimensions ; and a comparison of the wood- 
cuts (fig. 1) A, B, C, &c.,and A’, B’, C’, &c., which represent two series 
of sections of corresponding regions of the Human and the A¢eles’ 
brain, will at once show that the relative dimensions of the posterior 
cornu are greater in the Monkey than in Man. I may remark that, of 
the left hemispheres of three human brains which I have dissected for 
comparison with AZeles, that whose sections are represented in the 
figures had its posterior cornu far better developed than the other two, 
in one of which the cornu was a mere fissure, while in the other it was 
excessively short, not extending for more than half an inch behind the 
corpus callosum. 
Thus, not only does the posterior cornu of the lateral ventricle 
exist in Aze/es; not only has it that backward, outward, and then 
inward curvature which has been wrongfully asserted to be peculiar 
to the homologous cavity in the human brain ; but it is, in propor- 
tion, wider than in the human brain, and it is longer than in many 
human brains. 
The third point in my argument is the demonstration of the exist-. 
ence of the hippocampus minor. But such strange confusion has 
been lately introduced into anatomical science, partly by a misappli- 
cation of well-understood terminology, and partly, to all appearance, 
by a want of proper acquaintance with the structure and nomenclature 
of the human brain, that I must begin ad zzz¢z0, by a description of the 
latter, so far as regards the hippocampi and their related structures. 
VOL. IT KK 
