122 

 siJe of ths latar^l ventricle at the Isvjl of the pnllial iiver- 

 ticalan. 



The recessus neuropopicus of Burckharit ('9451) is of such 

 interest ^s to dssecy^e especial notice. It appears superfi- 

 cially as a ^ell-uarked depression in the median plane a little 

 anterior to the pallial eminences (F'ig.l, np.). It is render- 

 ed ev^en more noticeable during life by the penetration of blood- 

 vessels here, owing to which fact Rohon ('77) called it the 

 foramen nutritiuem. This structure is the vestige of a neuro- 

 pore. Its ontogeny was first described from the s^anoid brain 

 by vonKupffer ('90) as the lobus olfaotorlus impar. Rabl- 

 Riickhard describe! its development in the selachian embryo 

 ('93); and Burckhardt ('943) has identified it in many other 

 vertebrates. The recessus neuroporicus of Mustelus retains 

 the character of an open passage in the adult animal (F'ig.31, 

 np.), serving as a channel for blood- and lymph-vessels. It is 

 accompanied by a pair of fibre-tracts, right and left, which 

 take this primitive path from dorsum to base of the brain; see 

 Pig. 31, m.s.t. 



2, The Olfactory Lobe. 

 It is my purpose to devote a future paper to the entire 

 olfactory apparatus of Mustelus, and so a detailed description 

 of the olfactory lobe will not be ^iven here. For the under- 

 standing of what follows, it will be sufficient to state that. 



