121 



Thass p3culiarly corapactBi chHr.acteristics have been the source 



of no little controN^ersy. 3tujnick'-t has atteraptei to sho»» as 

 one of the iicta of a serie:5 of papers ( '94a, '94b, '95, '38) that 

 the selachian forebrain stands entirely apart from that of all 

 other vertebrates. His conclusions were drawn from stuiies on 

 Petromyzon, and they appear to rest apon a misconception as to 

 the exte-it of the tela choroidea superior. The fallacies of his 

 views have already been pointed out by Burckhardt ('94c), and 

 by Rabl-Riickhari ( '94). 



The lateral ventricles and the olfactory lobes of Mustelas 

 really anticipate the two-lobei condition of higher forebrains 

 in their essential characters. The lateral ventricles (F'ig.l) 

 are derived from the outer angles of the third ventricle, and 

 they pass the lamina ter-ninalis some distance apart from each 

 other. Their courses lie nearly parallel throughout. E^ach 

 gives off two diverticula, the olfactory ventricle and a dor- 

 sal branch, respectively. The dorsal diverticulum, (big. 31, 

 p. v.), is a short and narrow vertical cavity for the pallial 

 eminence; see Subsection 4. This stricture, while peculiar to 

 the brains of certain selachians, is nevertheless of some com- 

 parative value, as will be evident further on. 



The olfactory lobes are massive prolongations of the lat- 

 eral angles of the forebrain. The primitive character of an ol- 

 factory lobe is exhibited by the sharply defined bulbus and 

 tractus, and by the presence of tne olfactory ventricle (?ig. 

 31, ol.v.). This is a slender cavity derived from the outer 



