IOWA ACADEMY OP SCIENCE 
189 
THE FIFTH AND SEVENTH CRANIAL NERVES IN PLETHODON 
GLUTINOSUS. 
BY H. W. NORRIS. 
Thinking that possibly some of the conditions described by Dodds (1906) 
in the cranial nerves of Plethodon glutinous might throw some light upon the 
homologies of the ramus maxillaris V in the urbdele amphibians the writer 
was led to work out carefully the distribution of the fifth cranial nerve and its 
branches, together with those of the seventh nerve, in the same species. 
The material, small adults 35mm. long, was fixed in Vom Rath’s picro-acetic- 
osmic-platinic mixture, infiltrated and sectioned in celloidin, and studied en- 
tirely from cross-sections. Although the differential staining was not as thor- 
ough as the writer has usually obtained by this method with amphibian material, 
yet except for very minute branches its precision is reliable. 
According to Dodds there spring from the gasserian ganglion of Plethodon 
glutinosus three nerves: rr. mandibularis, maxillaris and ophthalmicus (pro- 
fundus). The rr. mandibularis and maxillaris arise together and pass out by 
a common foramen. I find that three nerves arise from the dorso-lateral border 
of the ganglion, one of which is the r. mand. Dorsal to the latter there emerge 
two others that evidently represent collectively the r. max. of Dodds. Accord- 
ing to the latter the r. max. branch “passes off laterally and curves forward 
in twm parts. One branch (infraorbital) breaks up back of the eye-ball, and 
the other (maxillary) passes forward a little above the maxilla.” Of these two 
nerves that I find leaving the gasserian ganglion dorsal to the r. mand. the 
dorsal one is distributed to the skin dorsal and posterior to the eyeball. The 
more ventral passes anteriorly until it comes in contact with the posterior 
border of the eyeball, where it divides into about five branches, of which two 
are distributed to the skin dorsal and anterior to the eye, while the other 
branches pass ventrally and are distributed to the skin ventral and anterior to 
the eye and dorsal to the mouth. Dodds is doubtless correct in interpreting 
these two branches as the r. maxillaris V. That in many cases they arise from 
the ganglion as a single nerve, as described by him, is probable. 
Dodds states that “the mandibular passes off laterally and soon curves ven- 
tralward to the maxilla, where it breaks up into three branches. Two of these 
remain in the upper jaw and pass forward well into the snout, one just external 
to, and the other just internal to the maxilla. * * * These two branches 
may possibly represent a part of the maxillary ramus. The third branch, about 
equal in size to the other two combined, passes ventralward into the lower 
jaw.” Such a distribution of the branches of the mandibular ramus as des- 
cribed by Dodds would be very unusual. I cannot agree with him as to the 
facts in the case. The r. mandibularis passes ventro-laterally from the gasserian 
ganglion and after giving off motor branches to the temporal, pterygoid and 
masseter muscles and a medium sized sensory branch to the skin, divides just 
