CRANIAL NERVES OF CHIMERA MONSTROSA. 665 



then very fine, and eventually passes on to the pharynx, terminating, after a long 

 course, a little behind the lower jaw in the mid-ventral line. During its course round 

 the arch it gives off two conspicuous nerves (IX 3) to the first demi-branch. 



(2) Post-branchial (IX 4). — Runs at the base of the second demi-branch for the 

 greater part of its course. On approaching the base of the first branchial arch, it runs 

 along its outer edge, and then turning sharply inwards and coursing along the inner edge 

 it reaches the pharynx. There it divides into anterior and posterior branches. The 

 posterior branch is short. The longer anterior branch runs obliquely forwards and was 

 lost at about the mid-ventral line, about an inch behind the lower jaw. The post- 

 branchial is a conspicuous nerve, but has no obvious branches. 



(3) Accessory skeletal branch (a) (IX 5). — Under this name I propose to describe 

 those branches of the glosso-pharyngeal and vagus supplying the visceral arches 

 themselves, and which are quite distinct from the prse- and post-branchial nerves. 

 These nerves, which I have found in all the cartilaginous fishes I have hitherto examined, 

 and which appear to have been previously overlooked, may arise from either the prse- or 

 post-branchial nerves, or may have quite a separate and distinct origin. They are 

 always closely applied to the arches they supply, and frequently pierce the substance of 

 the cartilage. In Chimsera they may arise at the same level as the prae- and post- 

 branchial nerves. The branch lettered IX 5 courses along the anterior edge of the first 

 branchial arch without giving off any conspicuous twigs, and ends at about the ventral 

 limit of the gill, breaking up into numerous fiue branches. It was not traced on 

 to the pharynx. 



(4) Accessory skeletal branch (b) (XI 6). — Courses along the posterior edge of the 

 first branchial arch, running parallel and being an accessory branch to XI 5. No big 

 twigs are given off, and it was not traced on to the pharynx. The branch lettered IX 

 7 was distributed to the second demi-branch. 



(5) Motor branch (IX 8). — The independent origin of this nerve has induced me 

 to describe it separately. It courses downwards and forwards, and divides into two. At 

 the point of division it dips down, and then runs sharply forwards under the hyoid arch, 

 and adhering to its inner face. Eventually it dips down still more and leaves the arch. 

 The anterior division (IX 9) runs forwards to supply the large levator muscle attached 

 to the anterior face of the hyoid arch. This is the main branch. The posterior division 

 (IX 10) supplies a small muscle attached to the posterior face of the hyoid arch. 



(6) Pharyngeal or visceral branches. — These nerves are peculiar in Chimsera, since 

 one invariably finds at least two to every branchial nerve. One of these nerves, how- 

 ever, is homologous in origin and distribution throughout the series, and will be 

 described as the visceral proper. The other pharyngeal branches will be described as 

 accessory visceral branches. The glosso-pharyngeal has only the latter, of which there 

 are three — all arising from the prse-branchial nerve (IX 11, 12, 13). The most slender 

 of these, however (IX 13), anastomoses with the second (IX 12). There are thus five 

 visceral branches of the glosso-pharyngeal of Chimsera — the continuations of the prae- and 



