1.M* PHYSIOLOGICAL SKKM->. 



The natifbnn eminence is much less prominent than it is 

 in the Three- toed Sloth ; and the bending of the rhinal 

 tU>ure is so slight that the whole fissure is approximately 

 horizontal. These two facts are probably correlated with 

 the peculiar absence of the so-called " Sylvian fissure" of 

 the Three-toed Sloth. Whilst it is surprising to find this 

 feature absent in the larger of the two brains, in which we 

 should expect it to be better developed, it seems to empha- 

 >i/e the morphological instability of this so-called " Sylvian 



Fig. 93. (Nat. size.) 



HIP.VEST. 



Fig. 94. (Nat. size.) 



PRIM. F. 

 CORP. QUADu 



COMMENT 



which a comprehensive survey of the Mammalia 

 M> clearlv demonstrates It also leads us to infer that \\liat 

 we may call the "feline type of Sylvian figure' 5 i- a mere 

 kink produced by meelianieal factors, of which the mo-t 

 important is the downward extension of the caudo-ventral 

 part of the neopallium. In Bradypu* where such an 

 extension has taken place (witness the ventral curve of the 

 posterior rhinal fissure!), tlii- so-called u Sylvian 



