DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 529 
of the lateral line system, merely the proximal part of several 
nerves not connected with that system has been outlined. In 
the trigeminal group the peripheral distribution of the ophthal- 
micus and buccalis profundus is shown, while the mandibularis 
is cut short, and its maxillary and mandibular branches are re- 
presented as arising much nearer the root of the main stem 
than is actually the case. The ophthalmicus profundus is seen 
to send several branches to the skin, which are lost in the 
vicinity of the supra-orbital line, thus connecting the nerve 
with the ectoderm of its origin. Asin the younger embryo, the 
ophthalmicus profundus divides distally into three main 
branches; one, of which only the beginning is represented in 
fig. 31, extends directly outwards between the nose and eye. 
The two remaining branches enclose the nasal epithelium, and 
are finally distributed to the skin of the snout. The anterior 
of these branches anastomoses with the ramus ophthalmicus 
superficialis, the posterior branch with the ramus buccalis 
facialis. The buccalis profundus is now distinct from the 
buccalis facialis throughout its entire length, and its branches 
are lost in the skin posterior to the infra-orbital line, as de- 
scribed by Dohrn (loc. cit.) in the Selachii. 
The two dorsai branches of the ophthalmicus superficialis 
facialis, which are seen in fig. 31 to supply the posterior and 
dorsal sense-organs of the supra-orbital lines, are of constant 
occurrence. At the end of the snout the superficialis breaks 
up into terminal branches, supplying the anterior cluster of 
sense-organs. 
In connection with the ramus buccalis facialis I would call 
attention to a dorsal branch which I have marked by a star in 
fig. 31. This branch supplies four sense-organs that probably 
belong genetically to the hyomandibular line. The dorsal part 
of the infra-orbital sensory ridge gives rise to a single line of 
sense-organs, and the nerve supplying organs in the same 
region as the four in question has been traced in another em- 
bryo to the ramus hyomandibularis. Thus the irregularity in 
the position of the sense-organs in Necturus is apparently cor- 
related with irregularity in their innervation, which is especially 
