1861 ] BRAIN OF ATELES PANISCUS. 249 



of a vertical section of an Jteles' skull ; but it is amply sufficient to 

 prove that, even accepting as the definition of the posterior lobe the 

 novel formula " All that part of the hemisphere which covers the 

 posterior third of the cerebellum and passes behind it," Ateles is 

 provided with a well-developed posterior lobe. 



In this respect, as I have already said, it resembles all the Old 

 and New World Simice which have yet been examined, — the only 

 genus, within my knowledge, which even comes near to presentino- an 

 exception being Mycetes. I have not, indeed, had the opportunity of 

 dissecting the brain of this monkey (nor has M. Gratiolet been en- 

 abled to give any account of it) ; but the Curator of the Hunterian 

 Museum having kindly permitted me to have a vertical longitu- 

 dinal section of the skull of a Mijcetes made, I found not only that 

 the plane of the tentorium ( and consequently the inferior margin of 

 the posterior lobes of the cerebrum) had a much greater inclination 

 than in any other Simian (making an angle of as much as 45° with 

 the base of the skull), but that the cerebral overiap, measured in 

 the manner described by me in the 'Atheneeum' for April 13th, 

 1861, does not exceed Jjjth of an inch, though the maximum length 

 of the cranial cavity is 2-4 inches. Notwithstanding this reduction 

 of the posterior lobe, however, the contrast between Mycetes, as a 

 true Simian, and a Lemur is very striking, especially if both be simul- 

 taneously compared vrith some lower Mammal, such as the Dog. The 

 occipital foramen in Mycetes is situated altogether upon the poste- 

 rior face of the skull, and the condyles look completelv backwards, 

 as in the Dog; while the occipital crest is placed as near' the postero- 

 superior margin of the skull as in that animal. In both, the poste- 

 rior face of the skull looks backwards, and not appreciably down- 

 wards. But in the Monkey the inclination of the tentorium, large 

 as it is, is far less than in the Dog. The inner face of the occipital 

 bone beneath the tentorium is not excavated, and the cerebral lobes 

 projected beyond the cerebellum when the palate was horizontal. In 

 the Dog, on the contrary, the internal surface of the occipital bone 

 below the tentorium is much excavated ; and, when the palate was 

 horizontal, the posterior edge of the cerebellum must have projected 

 far beyond the cerebral lobes. 



In Lemur catta the inclination of the tentorial plane is hardly 

 greater than in Mijcetes; but if the palatal line be made horizontal, 

 it will be found that the posterior boundary of the cerebellar chamber 

 projects for ith of an inch beyond that for the cerebrum, although 

 the greatest length of the cranial cavity is only 1-9 inch. In fact, 

 the cerebral hemispheres of the Lemur have a less backward develop- 

 ment than those of the Dog. I believe that all the Lemurs .are in the 

 same case, and that the Prosimice are sharply defined from the Simice 

 by the fact of always having more or less of their cerebellum un- 

 covered ; so that, by this character alone, the Lemurine brain is far 

 more widely separated from that of any Simian, than the latter is 

 from the human brain. 



While one American Monkey {Mycetes) is, if the development of 

 Its posterior lobes only be taken into account, at the bottom of the 



