34 



published in 1899 ^). At that time, very naturally, I looked upon these 

 nerves as of exceptional occurrence — possibly transitory in existence 

 and probably confined to a very limited number of species, but, more 

 light was to come, through the examination of the condition in other 

 selachians. In a later publication , under the title "A New Cranial 

 Nerve in Selachians" 2) , I described this newly observed nerve in six 

 genera^) and its developmental history in one*). 



During a residence at the Naples Biological Station, in 1902 — 03, 

 I had an opportunity to examine a considerable range of selachiaB 

 material and found the "new nerve" in adult specimens of 20 genera 

 and 27 species. This lifts the observations to a plane of greater in- 

 terest inasmuch as it shows that this nerve is of general occurrence 

 in selachians and that it persists in adult stages. 



I wish to express my thanks to the Director of the Station, and 

 to other members of the staff, for many courtesies and for the great 

 care taken in collecting material for my use. 



The nerves in question probably correspond, as will be noted later, 

 to those described by Pinkus in Protopterus, by Allis in Amia and by 

 Sewertzoff in embryos of Ceratodus. But there are differences between 

 the anatomy of this nerve in selachians, and in the forms mentioned — 

 notably in the fact that it has a ganglion in all the 27 species I have 

 examined, and differs in its peripheral distribution from that described 

 for Protopterus and Ceratodus. Sewertzoff described a ganglion in 

 embryos of Ceratodus, but neither Pinkus nor Allis observed a ganglion 

 in adult forms. 



In the selachians, so far as now determined, the new nerve is 

 connected peripherally with the olfactory epithelium and terminates 

 centrally in an eminence on the median septum which divides the fore 

 part of the brain cavity into right and left ventricles. My first im- 

 pulse was to look upon it as possibly representing an aberrant bundle 

 of the olfactory nerve, or, as an accessory element of the olfactory 

 system. The following anatomical descriptions, however, will show 

 that its fibers have no connection with olfactory glomeruli, and, that 

 throughout their course, they preserve a well-marked individuality. 

 This, taken in connection with the embryonic history, to be described 



1) LocY, New Facts regarding the Development of the Olfactory 

 Nerve. Anat. Anz., Bd. 16, No. 12, p. 273—290. 



2) The Mark Anniversary Volume. Boston, 1903. 



3) Squalus acanthias; Mustelus canis; Raja sp. ; Charcharias Htto- 

 ralis ; Sphyrna tiburo ; Scolidon terrse-novae. 



4) Squalus acanthias. 



