51 



of the slender tractus and upon the olfactory cup. Here it runs along 

 the anterior border of the bundle of fila olfactoria, and dips anoong 

 the latter, about midway between the posterior border and the antero- 

 lateral tip of the olfactory cup. In Raja, the fila olfactoria are more 

 compact and not obviously separated into two great divisions as in 

 the other forms described; there is, however, a median blood vessel 

 which partly divides them, on the surface, into parts which correspond, 

 I think, to those designated median and lateral in the other forms 

 examined. 



I have not traced the peripheral distribution of the fibers of the 

 new nerve in the skates. 



In sections of Raja, stained by Weigert's hsematoxylin, kindly 

 placed at my dispossal by Dr. 

 Strong of Columbia University, 

 both medullated and nonmedul- 

 lated fibers are shown. The 

 medullated fibers, of course, 

 stain in the Weigert and the 

 others do not. The fibres pass 

 deep into the mesial portion 

 of the prosencephalon, but, I 

 have not been able to follow 

 them to their central terminals. 



In Trygon pastinaca. 

 — In this form we have a com- 

 pact type of brain, the cerebel- 

 lum coming into contact with 

 the thalamencepbalon. The new 

 nerve connects, by two roots, 

 with the anterior dorsal surface 

 of the prosencephalon. It has 



Fig. 16. Brain of adult Trygon 

 pastinaca, nat. size. gn. slightly 

 magnified view of the ganglion of the 

 left side. B, ventral view of front 

 part of the brain of an adult Tiygon 

 violacea, nat. size, to show the noi'mal 

 position of the ganglion. 



^- 



y 



B 



a relatively large ganglion which in its undisturbed position, is packed 

 very closely in the angle between the tractus and the prosencephalon 

 (Fig. 16). It requires much fine manipulation to dissect it free from 

 the connective tissue strands and blood vessels. In front of the gan- 



4* 



