244 Journal of Comparative Neurology and Psychology. 



explained on the assumption that they belong to the central 

 grey. 



/^. T/ie nefves of Piatt, Locy and Pinkus. 



Miss Platt found in Acanthias (io6, 107) a process from 

 the neural crest at the groove between the mesencephalon and 

 diencephalon which later disappeared. She believed this to be 

 the vestige of a nerve which was formerly developed, and gave 

 it the name N. thalamicus. Its history has been followed more 

 completely by Hoffmann (58, 59). The strand of neural crest 

 cells descends over the optic stalk and meets the profundus 

 strand at a point where later the ciliary ganglion is formed, and 

 then loses its connection with the brain. Since the profundus 

 ganglion is distinct from the ciliary and is formed from a differ- 

 ent part of the neural crest, it seems altogether probable that 

 the ciliary ganglion permanently represents the N. thalamicus. 

 KuPFFER (79) finds the same structure forming the ciliary nerve 

 in Ammocoetes. Hoffmann describes a small cutaneous branch 

 from this ganglion but it is not clear that it is not composed of 

 profundus fibers. In the case of the ganglion ciliare we seem 

 to have the formation of a sympathetic ganglion from the gan- 

 glion of a nerve which has otherwise aborted. Since the 

 sympathetic is derived from the visceral sensory and motor sys- 

 tems, we may consider the N. thalamicus as the vestige of a 

 splanchnic sensory nerve root. In position it corresponds to 

 the second epiphysis and lies one segment in front of the pro- 

 fundus. It would therefore belong to the first mesencephalic 

 neuromere. The N. thalamicus may be considered as the 

 splanchnic sensory nerve of neuromere iv and head segment 4. 



Pinkus (104) described a nerve in Protopterus which arose 

 from the brain in the vicinity of the praeoptic recess and, run- 

 ning forward, was distributed to a part of the olfactory epithelium, 

 mingling with the olfactory nerve fibers. Locy (85, 86) has 

 described the development and anatomical relations of a nerve 

 which he has found in 19 genera of selachians. In most of the 

 genera described the nerve enters the ventral surface of the 

 fore-brain, in several it enters the dorsal surface near the anterior 



