268 Journal of Comparative Neurology. 



parison of Ampliibia with certain Selachia. In these fishes, as 

 Stannius ('49) and Herrick ('99, p. 321) point out, there is a 

 post-spiracular r. mandibularis intern us and a communis pre- 

 spiracular nerve which agrees in a striking manner with the r. 

 alveolaris of Urodela. This pre-spiracular nerve is shown nicely 

 in Squahis acanthias by Green's dissections ('00, p. 416). It 

 should be noticed that these two nerves in Squalus, the r. man- 

 dibularis internus and the "chorda tympani" of Green, inner- 

 vate areas which in part coincide and that the terminal fibers of 

 the two nerves anastomose. Here, then, are post-trematic and 

 pre-trematic neurones which have a common central termination 

 and a common area of distribution. Now, if we assume that 

 the amphibian facialis, in its phylogenetic development, has 

 passed through a condition similar to this found in Squalus, the 

 two amphibian types of the nerve may have arisen by a very 

 simple process of divergence from this hypothetical ancestral 

 type. Upon this hypothesis, specialization of the ancestral 

 pre-spiracular nerve with degeneration of the post-spiracular in 

 the Urodelian line, and specialization of the post-trematic with 

 degeneration of the pre-spiracular in the anuran line, would ac- 

 count for the r. mandibularis internus and the r. alveolaris with 

 their respective pecularities without violation of any of the 

 criteria of homology. 



On the above hypothesis, also, such a condition as that 

 described by Wilder for Siren lacertina, where the r. alveolaris 

 arises from the r. palatinus (Wilder's palatinus anterior), be- 

 comes perfectly intelligible. Indeed, this condition is very like 

 that found in Squalus. From this point of view, again, the r. 

 alveolaris and the r. mandibularis internus would not be expected 

 to agree in their relation to the glossopharyngeus and trigeminus. 

 This explanation of the conditions, I believe, is adequate and 

 in accord with the facts. 



With regard to the relation of these amphibian nerves to 

 the mammalian chorda tympani, it must be admitted that there 

 is a wide gap between the Amphibia and any mammal the 

 cranial nerves of which have been adequately studied for pur- 

 poses of comparison from the point of view of nerve compo- 



