522 H. W. NORRIS AND SALLY P. HUGHES 



passes into a canal at the medial border of the nasopremaxilla 

 on the ventral wall of the nasal chamber (figs. 3-1). After 

 some anastomoses with terminal branches of the medial ramulus 

 of the ramus maxillaris V, it is distributed to the ventral epi- 

 thelium of the snout, anterior to the tentacular pit. From the 

 point of origin of the last-named nerve {op.2v) anteriorly there 

 are given off from the main ramus numerous twigs to the skin 

 on the top of the head and snout. The final destination of the 

 main ramus (op.2) is to the skin of the ventral side of the tip 

 of the snout. 



6. General reflections upon the trigeminal nerve 



The distinctness of the Gasserian and profundus ganglia from 

 each other is apparently accompanied by a sharper delimitation 

 of the peripheral portions of the nerves than occurs in other 

 amphibian groups. The almost complete absence of lateral-line 

 components in the adult condition makes for greater independ- 

 ence of the fifth and seventh nerves, and produces a simpler 

 structure. Of significance is the lack of an anastomosis between 

 the ramus ophthalmicus profundus V and the ramus palatinus 

 VII, and the presence of an anastomosis between the maxillaris 

 V and the palatinus VII. In the Urodela the former anastomo- 

 sis occurs; in the Anura both types occur. In Siren, as the 

 writer has pointed out ('13), somatic sensory fibers pass from 

 the maxillaris V into the palatinus VII. 



The ramus maxillaris in caecilians is significantly large as 

 compared with the corresponding nerve in Urodela. Its anas- 

 tomoses with the ramus palatinus suggest that it carries fibers 

 which in the Urodela run in the ramus ophthalmicus profundus. 

 The distinctness of the profundus from the Gasserian ganglion 

 in caecilians may be responsible for this seeming transfer of the 

 palatine anastomosis from the profundus to the maxillaris. The 

 lateral division of the ramus maxillaris in caecilians has about 

 the same distribution as the entire ramus maxillaris in the uro- 

 deles; the medial branch which contributes to the palatine anas- 

 tomosis in the caecilians is distributed to territory that belongs 



