CoGHiLL, Cranial Nei-ves of Ambly stoma. , 279 



(Herrick, '99, p. 257). It is doubtful, however, that there is 

 any genetic relationship between these anastomoses in Urodela 

 and fishes. 



It may be of interest, also, to notice the parallelism which 

 exists between the anastomoses just mentioned for Ambly- 

 stoma and the well known anastomoses between the nerves 

 which supply the external gills. The first gill, which is born 

 upon the first branchial arch, receives a nerve which is formed 

 by fusion of branches from the t. glossopharyngeus and the 

 first t. branchialis X. The second gill, which is supported 

 upon the second branchial arch, receives a nerve which is 

 formed by fusion of branches from the first and second tt. 

 branchiales X. The third gill receives a nerve from the second 

 t. branchialis X which sometimes, probably typically, fuses 

 with a branch from the second spinal. The parallelism between 

 these two series of anastomoses is so striking that one is 

 tempted to attribute it to some genetic relationship between 

 the two series. Such an interpretation, however, would 

 involve the assumption that my fifth branch of the first t, 

 branchiahs X and third branch of the second t. branchialis X 

 are pre-trematic nerves. But these nerves are largely motor 

 while the typical pre-trematic nerve is sensory only. Further- 

 more, the external gill is considered ectodermal in origin and 

 not a derivative of the internal gill of the fish. I believe, 

 therefore, that the anastomoses of the nerves to the exter- 

 nal gills are the result of adaptation, and that the pres- 

 ence of a nerve from the first t. branchialis vagi in the first 

 external gill, a structure born upon the first branchial arch, 

 does not warrant the conclusion that the nerve is pre-trematic 

 in function. If this conclusion is correct, the parallelism 

 between the two series of anastomoses in question is only 

 accidental. 



6. — Rami Post-trematici. 



The relation of the t. glossopharyngeus to the m. cerato- 

 hyoideus externus in Urodela has already been discussed in 

 connection with the r. jugularis VII. The m. cerato-hyoideus 



