tailless catarrhine apes of the old world, the cerebral hemispheres project for back beyond the cerebellum, though the latter is very well developed—in fact, as the cerebral hemispheres project nearly a centimetre behind the cerebellum, while the whole brain is only 512 centimetres long, the backward projection of the third lobe is, in this monkey, relatively greater than in man.
The "Transactions of the Royal Netherlands Institute at Amsterdam for 1849" contain one of the most valuable memoirs on the cerebral organization of the higher apes that has yet been written, entitled, "An Anatomical Investigation of the Brain of the Chimpanzee," by Schroeder van der Kolk and Vrolik. In their two plates they represent the brains of a chimpanzee, an orang, and a new-born child, and, in all, the letter c is applied to the same part—the posterior or third lobe, which they term "achterhoofds-kwab," "occipital lobe," in the explanation of the plates, or frequently in the text, "achter-kwab," "posterior lobe"; nor among the heads of their careful enumeration of the differences between the brain of man and the higher apes does any one of the three differential characters whose existence I have denied find a place.
Finally, in the preface to the most elaborate special memoir that has yet appeared upon the conformation of the brain in the higher Mammalia—the "Memoire sur les plis Cérébraux de l'Homme et des Primatés," by M. P. Gratiolet,—I find the following passage (p. 2):—
"The convoluted brain of man and the smooth brain of the marmoset resemble one another in the fourfold character of a rudimentary olfactory lobe, a posterior lobe, which completely covers the cerebellum, a well-marked fissure of Sylvius, and lastly, a posterior cornu to the lateral ventricle. These characters are met with in combination only in man and in the apes."
M. Gratiolet's beautiful original figures of the brain of the chimpanzee (Pl. vi), and of the orang (Pl. vii), show quite clearly that the hinder margin of the cerebral lobes in these animals; when the brain is in its natural condition, overlaps the hinder margin of the cerebellum.
Many months ago, having learned that my friend Dr. Allen Thomson had at one time occupied himself with the dissection of the brain of the chimpanzee, I applied to him for information, and he has very kindly allowed me to print the following extracts from his letters. Of the first brain he examined—that of a young female chimpanzee, seven or eight months old,—this eminently careful anatomist and physiologist says (under date of May 24, 1860):—
"There is, very clearly, a posterior lobe, separated from the middle one by as deep a groove between the convolutions on the inner side of the hemispheres, as in man, and equally well marked off on the other side. I should be inclined to say, that the posterior lobe is little inferior to that of man, excepting, perhaps, in vertical depth. The cerebral hemispheres completely covered the cerebellum, as seen from above. I took pains to observe this while the brain was still within the cranium, looking down upon it at right angles to the longtitudinal axis of the cranial cavity, and I found the posterior extremity of the cerebral hemispheres projected a little beyond the vertical line, passing the back of the cerebellum."
