134 THE SALAMANDER 



the cranial nerves of their native Urodeles by means of serial sections, 

 paying particular regard to the distribution of their several compo- 

 nents. These accounts, notably that of Coghill (1902) for Ambly- 

 stoma, have been found to be of considerable use in unravelling 

 the intricacies of the nerve relations in the head of the Salamander. 

 After making due allowance for the absence of a lateralis component 

 in the adult Salamander, the correspondence between the cranial 

 nerves of this animal and those of Amblystoma is very close 

 indeed. 



The present account is based almost entirely on observations made 

 by actual dissection carried out under a binocular dissecting micro- 

 scope — checked in a few cases by microtome sections. No attempt 

 has been made to elucidate the components of the various nerves, but 

 these may be deduced by analogy from the descriptions of American 

 Urodeles above referred to, and the composition of each nerve thus 

 deduced has been given in parenthesis. It should be noted further 

 that where the words 'origin' and 'root' are used they refer only to 

 the point of emergence of the nerve from the surface of the brain and 

 not to the deeper origin within it. 



All cranial nerves are paired, and those of one side only are 

 described. 



2. Description. 



I. N. Olfactorius (n.i). The first cranial nerve leaves the 

 olfactory lobe of the prosencephalon from its ventro-lateral border 

 and passes directly forwards, through the fenestra olfactoria, into the 

 nasal capsule. It is a flat oval in transverse section. Almost imme- 

 diately after separating from the brain the nerve gives off a branch 

 from its ventral side which turns sharply outwards towards the 

 internal narial opening, and apparently supplies Jacobson's gland. 

 The main olfactory nerve then divides into a dorsal and ventral 

 branch, each of which ramifies over its respective surface of the nasal 

 sac, supplying the olfactory epithelium. 



II. N. Opticus (n.2). The optic nerve passes from the floor of the 

 thalamencephalon and is inclined slightly anteriorly and dorsally. 

 It leaves the cranial cavity by the optic foramen in the side wall of the 

 cranium. Since the nerve occupies only a very small part of this 

 'foramen' it would perhaps be more correct to call the latter the optic 

 fenestra. The nerve is protected within the fenestra, and during 

 its passage from the side of the skull to the bulbus oculi, by a 

 strong, fibrous, connective tissue sheath, the whole structure 

 forming the optic peduncle. 



