CRANIAL NERVES OF CHIMERA MONSTROSA. 655 



supplies the first 8 sense organs of the infra-orbital line, and also the most ventral of 

 the ampullae opening on to the surface by the large occipital pores (see fig. 1). The 

 remainder of these ampullae are, I believe, innervated from the superficial ophthalmic. 

 After entering the orbit the buccal is soon resolved into two large bundles. The ventral 

 bundle ultimately separates out as the inner buccal, whilst the dorsal one, passing under 

 the ventral, becomes the outer buccal. The inner buccal pursues a forward sigmoid 

 course, and gives off 22 branches, supplying the inner buccal group of ampullae and the 

 26 sense organs of the dorsal division of the infra-orbital line. The outer buccal divides 

 into two branches. The posterior, after giving off anastomotic twigs to the maxillary, 

 divides into seven bundles supplying the first 8 sense organs of the ventral division of the 

 infra-orbital line. The anterior branch, after sending a twig to the inner buccal group 

 of ampullae, divides into 7 bundles supplying the outer buccal group of ampullae and the 

 remaining 6 organs of the infra-orbital line. The outer buccal group of ampullae curiously 

 differs from the inner buccal and superficial ophthalmic groups, in that the ampullae, whilst 

 being of the same compound nature, are only about half the size. They are, however, 

 larger than those in the mandibular groups. 



(3) External Mandibular. — The origin of this nerve from the hyomandibular trunk 

 has been already described (see p. 651). It is connected with two groups of ampullae — the 

 mandibular and hyoid groups of Ewart, and thus consists of two divisions — an anterior 

 and a posterior. The latter division is in a somewhat curious condition. It has only a 

 very few ampullae connected with it, and breaks up into a plexus supplying a peculiar 

 gelatinous tissue lying immediately above and slightly behind the muscles supplied by 

 the post-branchial division of the facial. Only very few typical ampullae were identified 

 in this tissue, which probably, therefore, represents a degenerate group, connected perhaps 

 with the aborted spiracle. The external mandibular (posterius) sends several small 

 twigs to the skin, and anastomoses with the post-branchial division of the Vllth. It 

 must therefore contain fibres from the facial proper. From its posterior surface it gives 

 off six twigs, which supply the 7 sense organs of the posterior division of the hyo- 

 mandibular canal. The external mandibular (anterius) courses downwards and forwards, 

 and gives off from its anterior edge the four twigs which, with two others given off from 

 the posterior edge of the nerve further down, supply the 11 sense organs of the anterior 

 division of the hyomandibular canal. On arriving at a level dorsal to the angle 

 of the jaw, the ext. mandibular anterius breaks up to supply the mandibular group 

 of ampullae,* which, though small, is very compact, and lies under the skin behind the 

 lower jaw, almost on the mid- ventral line. These ampullae are smaller than any of those 

 found in the snout, and have not the compound structure of the latter, being simple and 

 kidney-shaped, with the nerve entering at the hilus. Three facts must be noted : — (a) 

 several twigs are given off to the skin ; (6) there is an anastomosis with the mandibular 

 division of the Vth as described by Stannius — both these nerves must be considered to 



* First discovered by Ewart (58, p. 77). 

 VOL. XXXVIII. PART III. (NO. 19). 4 Y 



