328 PROF. G. ELLIOT SillTTI OX THE 



about lialf as hroad, lying in contact witli the under surface of the eerebral hemisphere 

 except in the anterior lo mm. of its extent *. 



Its posterior end is joined to a flattened peduncle Avhich is as broad as the bulb itself. 

 It is very short, for it pursues a course of only 3 or i mm. before it becomes attached to 

 the base of the cerebral hemisphere. In tliis respect it differs most decidedly from the 

 very long and attenuated olfactory peduncle of the Apes ; but, oa the other hand, a short 

 thick peduncle like that of the Lemur is found in the vast majority of mammals, and 

 must be regarded as the common mammalian type. 



The lateral half of the peduncle is covered by a dense thick l)undle oO fibres which 

 constitutes the tractus olfactorius [lateralis]. Tliis white covering also extends over the 

 lateral border of the pediincle. The internal half of the ventral surface and the mesial 

 border present a greyish appearance, because the medullary fibres of the so-called mesial 

 tract are much less numerous and more scattered than those of the lateral tract. In the 

 elongated peduncle of all Monkeys the whole peduncle appears to consist of nerve-tibres, 

 so that its real constitution is not so obvious as it is in the Lemurs. 



Just behind the insertioa of the olfactory peduncle into the base of the hemisphere 

 there is a transversely -placed, oval, puckered area of grey sul)stance, 4 mm. broad 

 and about 2-5 mm. in the sagittal direction. This is the tuberculum olfactorium — 

 a pecvdiar cortical formation coating the ventral surface of the head of the corpus 

 striatum. The features of this body are exceedingly constant thi'oughout the Mammalia, 

 l)ut become somewhat obscured in the adult In-ain of Man and the Anthropoid Apes. 

 The mesial surface of the olfactory peduncle extends on to the corresponding surface of 

 the hemisphere just in front of the tuberculum olfactorium. 



The lateral wall of the olfactory peduncle is prolonged backward into continuity with 

 the pyriform lobe. The latter begins in front as a narrow horizontally placed grey band 

 3 mm. wide, the internal part of which is covered I)y the (external) olfactory tract. 

 Opposite the outer extremity of the tuberculum olfactorium it becomes bent at right 

 angles upon itself (ilg. G) and at the same time broadens to almost four times the width, 

 so that its posterior iTM-t forms a very prominent rounded boss projecting 4 mm. below 

 the level of the ventral surface of the anterior part. The transverse depression formed 

 by this sudden bend is the vallecula Sylvii — a furrow which is quite distinct from the 

 fossa and iissura Sylvii. 



The vallecula Sylvii is much deeper and n\oie pronounced in the L^nuu- than in most 

 mammalian brains of other orders. In some of the smaller Xew- World A]jes, such as 

 the Hapalidie, the vallecula presents features exactly analogous to that just described, 

 the posterior pavt of the pyriform lol)e being bent at an angle of S)(K on the anterior 

 part ; but in most Apes the angle of bending hecomes much more acute, the posterior 

 part biilges forward over tlie anterior part of tlie pyriform lobe ; and the vallecula Sylvii 

 becomes a very deep cleft, which is commonly regarded as part of the stem of the true 

 Sylvian fissure. 



* These measuremeuts refer to a fresh specimen of Lemur ftihiis, and may be regarded as a fair average of all 

 the specimens of the genus Ltinar which 1 have examined. 



