CRANIAL NERVES OF CHIMERA MONSTROSA. 653 



off posteriorly ; the other, which is the direct continuation of the nerve after giving off 

 the above plexus, comes up to the surface and courses over the outer surface of the same 

 muscle, and supplies its ventral portion, the dorsal moiety being supplied by the post- 

 branchial C. 



(b) Given off shortly after the origin of (a). It dips down and runs forwards and 

 downwards, and, after a somewhat extended course, anastomoses with the chorda tympani. 



(c) Origin described above. Euns downwards and forwards, and becomes embedded 

 in the extensor muscle of the hyoid arch,— i.e., the muscle which draws the arch 

 forwards, and thus increases the width of the cleft. 



(4b) Post-branchial C* — This nerve, which = the remainder of the 'ramus opercu- 

 laris,' soon divides into two main branches, both of which course straight downwards, 

 and break up to form an elaborate plexus. This plexus is continued round to the mid- 

 ventral line, and lies mostly over the anterior gill clefts. It supplies the superficial 

 muscles (l) of the opercular fold, and (2) of the bocty wall overlying the gill clefts in 

 front of the opercular fold, and between the latter and the mouth. 



My reasons for describing the nerves Aa and 46 as being equivalent to the post- 

 branchial division of the Vllth, are, I think, obvious enough. The post-branchial of the 

 facial should, as is well known, course along the anterior edge of the hyoid arch, and 

 supply its muscles ; and since the opercular fold of Chimsera is associated with the 

 hyoid arch, and is supported by cartilages borne on that arch, I think it will be admitted 

 that these two nerves fulfil the requirements of the above definition. The facial nerve 

 of Chimsera, therefore, despite the absence (?) of the spiracle, only wants a dorsal 

 sensory branch to be comparable to the other branchial nerves. 



H. The Lateral Line Nerves. 



I distinguish in this system the following five nerves : — 



(1) Superficial ophthalmic. 



(2) Buccal. 



(3) External mandibular. 



(4) Lateralis. 



(5) Auditory or ' eighth ' cranial nerve. 



(1) Superficial ophthalmic. — Arises from the medulla by a large ventral root situated 

 behind the root of the hyomandibular, and below and behind the root of the auditory 

 (see figs. 1 and 3). This root has been figured by Schwalbe (23). It courses upwards 

 and forwards, passing over the root of the buccal nerve. After it has passed the buccal 

 it receives a large bundle of fibres from the anterior edge of the latter, so that the super- 

 ficial ophthalmic may be said to have both dorsal and ventral roots. There is a 

 triangular space inclosed by the root of the buccal and the dorsal and ventral roots of 



* The ' internal mandibular ' (with post-branchial B (?)) of Stannius. 



