DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 530 
nerves after their fusion supply the lateral musculature, the 
vascular system, and the skin, including the external gill. The 
distribution of the two serially homologous branchial branches 
of the first vagus arch is similar. The dorsal vagus nerve sends 
branches to the upper branchial muscle, through which it 
passes, before dividing into branches of the commissural and 
epibranchial lines. The main branchial nerve of the posterior 
vagus arch arises from the ganglion near the origin of the 
nerve of the anterior arch. The two pharyngeal nerves (cut 
off in the reconstruction) that arise from the vagus are dis- 
tributed by numerous branches on the pharynx in their imme- 
diate neighbourhood. 
In regard to the dorsal and median trunk lines I have 
nothing to add. From the ventral nerve of the lateral line a 
few large but short motor branches arise, and a longer branch, 
which supplies the ventral branchial muscles, is evidently serially 
homologous with the three preceding post-trematic nerves. 
In regard to the morphological value of the facial nerves 
there is great difference of opinion. I believe, however, that 
the development of the ramus ophthalmicus superficialis and 
ramus buccalis in Necturus demonstrates that neither nerve 
can be considered segmental. Of the ventral facial nerves, 
v. Wijhe tells us (38, pp. 313, 314) that the ramus mandibularis 
(my hyomandibularis) always divides into an external and 
internal branch, and evidently does not belong to the hyoid 
arch, as does the ramus hyoideus, but to an anterior visceral 
arch. Therefore, if the ramus hyoideus represents a posterior 
branch (post-trematic), one would be inclined to regard the 
ramus mandibularis as an anterior branch; but for this it 
would be necessary that its course should lie on the anterior 
wall of a gill cleft, which is not the case, as the spiracle is 
found anterior to the nerve. Two possibilities exist; either the 
ramus mandibularis is still a ramus anterior, and the gill cleft 
before which it should lie has aborted, or this is not the case, 
and the nerve is a secondary outgrowth. If a gill cleft has 
aborted between the ramus mandibularis and ramus hyoideus, 
it probably was situated between the parts of the hyoid arch, 
