So ZOOTOMY. 



fibres to the upper jaw : the main part of the mandibular nerve goes to 

 the sensory tubes in front of the antorbital cartilage : the mandibular 

 goes to the lower jaw (outer side), but also sends a large branch to the 

 upper jaw. There is, however, endless variation in the distribution of 

 these nerves. 



XLVI. Carefully slice away the cartilage forming the 

 roof of the auditory capsule, taking care not to 

 injure the membranous labyrinth ( 213); dissect 

 away the connective tissue, &c., from the hyo- 

 mandibular, and the muscles on the floor of the 

 orbit, making out 



211. The hyomandibular nerve, or posterior branch 

 of the seventh (Fig. 22, Vli rb ): after leaving the cranial 

 cavity it curves round the anterior border of the auditory 

 capsule, and passes almost directly outwards, over the 

 hyomandibular cartilage and behind the jaw muscles, break- 

 ing up at last into a number of fibres which are distributed 

 to the large sensory tubes situated in front of the gills. As 

 the hyomandibular nerve passes the jaw muscles, it gives off 

 two small branches (c.ty), which represent the chorda 

 tympani of the higher animals, and are distributed to the 



inner surface of the lower jaw. 



212. The palatine nerve (Fig. 22, 7/77*), or anterior 



division of the seventh, which separates from the common 

 root of the seventh soon after its exit from the skull, passes 

 in front of the spiracle, and breaks up into a number of 

 branches, some of which are distributed to the mucous 

 membrane of the mouth and others to the pseudobranchia. 



213. The membranous labyrinth (Fig. 28) or 

 internal ear, a delicate apparatus enclosed within the auditory 

 capsule, and consisting of a large sac or vestibule (7;), 

 and three semicircular canals, one of which is anterior 

 and vertical (a.s.c\ another posterior and vertical (p.s.c), and 

 the third horizontal (h.s.c). 



