138 

 which thsss fishes place upoti the olf-ictory app^ritus in the 

 search for fool. In higher vertebrates, as the olfactory sense 

 becomes linkei to the palliam through stronger bonds, and as 

 other senses make pallial connections, one after another, this 

 part of the brain takes on functions of an ever hii?her value. 

 In Mustelus, there is merely an anticipation of pallial possi- 

 bilities. 



■'). SuDDor tiig Elements. 



Both neurogliar and ependymal elements are present in the 

 forebrain of Viustelus. 



Ependyma is found r^idiating from every part of the later- 

 al ventricle, and its characters are nearly uniform for the 

 several regions. The ependymal cells have their nuclei situa- 

 ted at slightly different levels, and so a broad zone next to 

 the ventricle presents chiefly nuclei. The shape of the cell- 

 body is influenced by the position of its nucleus, of course, 

 bit the broadened part is usually not directly in contact with 

 the ventricle. The ependymal fibre runs straight outward from 

 the cell-body, as a rule, and it reaches entirely to the lira- 

 itans externa. It does not branch, its size remains nearly 

 uniform, and its course is only slightly irregular. It bears 

 a greater or less profusion of delicate, mossy twigs of short 

 length. The inner portions of two ependymal elements are shown 

 in Pi^.42. 



