200 Journal of Comparative Neurology. 



determination should be much easier than in the more highly- 

 specialized Anura. 



Netvus abducens. The sixth nerve (a. b. d.) is not, as in Sal- 

 amandra maculata, the smallest of the cranial nerves. It arises 

 on the ventral surface of the medulla under the origin of the 

 ninth by several small roots, whose combined trunk contains 

 about 50 fibres, thus exceeding the size of the trochlearis. 

 This trunk passes laterally and forward, lying directly beneath 

 the main root of the trigeminus. Its subsequent course is very 

 much as in the common frog. It enters the Gasserian ganglion, 

 but leaves it again immediately in company with the ramus 

 ophthalmicus trigemini. Some of the fibres uppear to pass 

 from the entering root directly to the emerging root without 

 entering the ganglion. Peripherally it divides into two branches, 

 as in the frog, one for the m. rectus externus, the other for the 

 m. retractor bulbi (r. b.) The ciliary branches described by 

 Ecker for the frog were not found. Although the two branches 

 of the sixth nerve are indistinguishably blended when they leave 

 the Gasserian ganglion, yet it would seem that the branch des- 

 tined for the m. retractor bulbi ought not to be assigned to this 

 nerve, but to the trigeminus ; for the root leaving the ganglion 

 is nearly twice as large as the root entering it. Moreover the 

 branch passing to the m. rectus externus is about the size of 

 the sixth root proximally of the ganglion. The exclusion of 

 the branch to the retractor bulbi from the abducens finds a fur- 

 ther justification in the fact that in Salamandra maculata this 

 muscle is not innervated from this nerve, though in that case it is 

 the oculomotor which assumes this function. 



The trigeminus differs widely from that of Salamandra mac- 

 ulata in many important repects. The nerve arises in two di- 

 visions, a large ventral root (V) and a smaller dorsal root (d) 

 which serves also as the dorsal root of the facial. These roots 

 unite to form a large Gasserian ganglion from which three rami 

 are given off, a ramus ophthalmicus, a ramus fronto-maxillaris 

 and a ramus mandibularis. The first of these passes directly 

 forward from the ganglion ; the other two pass directly laterad 

 lying in immediate contact and apparently freely anastomosing 



