14 'Jounial of Comparative Neurology and Psychology. 



2. The Fore-braiii of the Selaehiajis. 



The fore-brain of the selachians is distinguished from that of 

 the teleosts especially by the development of nervous elements in 

 the pallium. The degree of this development, however, varies 

 with the species examined. While the Rajidae, as well as Pris- 

 tiurus and Lamna, have a pallium so extremely developed as even 

 to obliterate completely the ventricles w^hich are so enormously 

 spacious in the teleosts, the Holocephali and Notidanidae have 

 large fore-brain cavities, whose pallial covering remains for quite 

 considerable part still membranous, as appears from the descrip- 

 tion given by Wilder of Chimaera monstrosa, and especially from 

 the excellent comparative investigations made by Burckhardt. 



The fore-brain of the Notidanids (Heptanchus, for instance) 

 is nearly the same as far as this point is concerned as that of 

 Chimaera, in whose pallium it is the lateral parts chiefly which have 

 developed such nervous masses. The selachians, Galeus canis 

 and Angelus squatina, whose fiber tracts I have examined, present 

 a pallium whose thickness surpasses the breadth of the ventricles. 

 This is especially the case with Angelus squatina, in which respect 

 I quite agree with Botazzi. 



In this selachian the relations of the lateral ventricles are very 

 simple as shown by Fig. xii, a to /, and there is no ventricle in the 

 lobi olfactorii. This is not the case with Galeus canis (Fig. xiii, 

 a to /), as also described by Houser (who names this species 

 Mustelus canis). Houser has already mentioned that, although 

 the lateral ventricles are small here, they show, in addition to their 

 olfactory evaginations, also a small dorsal evagination which he 

 calls the diverticulum dorsale, an unobjectionable name which 1 

 adopt. The presence of this ventricle brings ir about that the 

 lateral ventricle of Galeus, midway of its length, presents at the 

 same place two evaginations (Fig. xiii, h), one rather large extend- 

 ing into the lobi olfactorii, and the other smaller going dorsad only 

 a short way, the diverticulum dorsale. The lateral ventricle con- 

 tinues as a narrow fissure and terminates far forward, after having 

 (between / and c) expanded, due to the fact that here (Figs, xiii, 

 d; and xvii) there terminates a medial protrusion of its wall, about 

 which I shall speak later. 



Since it is impossible to distinguish the different areas of the 

 fore-brain of Galeus morphologically, as in the teleosts, I proceed 



