.A[O]{IMI0LOGY OF THE BKAT\ IX TliF. .M A.MAr.UJA. 12-") 



the Anteatei's there is anotlier peculiar Primate feature^: the suprasylvian and pseudo- 

 sylvian sulci blend to form a Sylvian lissure. it is quite impossible to say how much 

 importance is to be attached to such ])henoinena. 



After seeking for some explanation for ail the apparently conflicting features of the 

 Prosimian brain, the following tentative working hypothesis as to the ancestry of 

 the Lemurs shaped itself in my mind, and I ins(>rt it here merely as a slender bond 

 connecting certain facts scattered throngh these notes. 



The brain of the Primates was derived from some lusectivore-like type, tiie cerebral 

 hemispheres of Avhich attained a precocious development and, as one of the expressions 

 of their greatness, bulged backward over the cerebellum. In consecpience of this great 

 extension of the " physical organ of the associative memory of visual, auditory, a-ivd 

 tactile sensations," the sense of smell lost the predominance which it exercised in th(> 

 piimitive mammal (and in all the Orders of recent mammals), and the olfactory parts of 

 the brain rapidly dwindled. This early Primate developed its distinctive type of 

 calcarine sulcus and " Sylvian lissure," the lateral, coronal, ajid orbital sulci, and 

 the characteristic central sulcus. 



In the keen struggle for existence, the Lemurs ceased to keep pace with the other 

 Primates so far as the increase in the size of tlie brain is concei'ncd. Thev became 

 more specialized, and their brain prol)ably shrunk, thus leading to a retraction of 

 the occipital pole of the hemispheres. 



AVith the diminution of the size of the neopallium the sense of smell comes to play 

 a more important part, and a secondary re-enlargement of the olfactory regions occurs. 

 The blotting-out of the rliinal fissure may be an indication of this jjhenomenon. 



This somewhat crude and tentative scheme is put forward to give expression to 

 the view that the Lemurs are highly sj)ecialized Primates which share most of their 

 brain-features in common with those of the Apes, and that some at least of the 

 apparently primitive characters may be due to a secondary retrogressive modification of 

 a more highly-developed type of brain. 



ADDENDUM.— The Cerebellum. 

 (Pteceived April 21, 1002.) 



In my account of the brain in the Edentata*, I called attention to the fact (which 

 had previously been recognized independently by Stroud and Kuithan) that underlying 

 the apparently irreconcilable differences and seemingly divergent designs exhibited in 

 the cerebellar architecture of mammals, there is one common fundamental plan which 

 becomes variously elal)orated in its details in different animals. 



In attempting to describe the cerebellum in the Edentata I found that the nomcnclatiuv! 

 and mode of subdivision usually adopted in works on Human Anatomy were so 

 ill-adapted to the needs of Comparative Anatomy, that it was quite impossible to describe 



* '• Thf Liiiiiu in the Edentata," Trans. Linn. Soc. ser. 1', Zool. voL vii. IS'JO, pp. 3G0 et si'q. 



61* 



