﻿lxxil PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [MayipIO, 



particular, he remarks that if a composite picture were obtained by 

 superposing outline drawings of its topography taken from a number 

 of examples, then this would show sharper furrows than in the 

 chimpanzee and make a very close approach to the arrangement 

 existing in Man. The brain of the chimpanzee presents the next 

 closest alliance with that of Man, and that of the orang follows at 

 no great interval. A gap then intervenes separating off the gibbon, 

 which, as regards the anatomy of its brain, is more closely con- 

 nected with the lower Catarrhine monkeys than with the man-like 

 apes. 



In thus speaking of the brain reference is intended to the cere- 

 brum only ; Prof. Bolk has also made a comparative study of the 

 cerebellum as it occurs in the Primates, and finds evidence of an in- 

 creasing resemblance to Man as its structure is traced upwards from 

 the lower apes. 1 The cerebellum of the lemurs is said to present 

 characters which distinguish it from the fundamental type of the 

 Primates, and these are said to have been inherited from a pre- 

 lemuroid ancestor. The general plan of the Primate cerebellum is 

 first met with in the Arctopithecini (marmosets) ; from this we pass 

 to the Platyrrhine and Catarrhine monkeys, which closely resemble 

 each other in the characters of the cerebellum ; from the Cerco- 

 pithecidee there is a transition to the gibbon, and from the gibbon 

 to Man. The cerebellum of the chimpanzee makes a nearer 

 approach to that of Man, and still nearer comes the cerebellum of 

 the orang. No mention is made of the gorilla, which does not seem 

 to have been investigated. 



The relations of the brain of the lemurs to that of the other 

 Primates has been made the subject of an exhaustive study by 

 Elliot Smith. 2 These animals are now extremely specialized, and 

 are more especially distinguished from the apes by the large size 

 of their olfactory organs. In connexion with this specialization 

 some of their cerebral characters, such as those that indicate a 

 marked divergence from the Primate stem, for instance, may have 

 arisen as comparatively late acquisitions. Elliot Smith remarks 

 that the brain of the lemurs can only be explained by supposing 

 that it had first made a fair advance along the main stream of the 

 Primates, and then suffered a retrogressive development. 



It is interesting to note that the fronto-orbital and paracalcarine 

 sulci, which occur both in the lemurs and in some of the larger 



1 'Das Cerebellum der Saugetiere ' 1906. 



2 ' On the Morphology of the Brain in the Mammals ' Trans. Linn. Soc. 

 1902, p. 312. 



