82 ZOOTOMY. 



muscles, on the dorsal side of the spinal nerves (§ 222). 

 The branchial nerves (br. 2 — 5) are four in number, and 

 are given oif opposite the four posterior gill clefts. Each 

 one, soon after leaving the vagus divides into two branches, 

 one of which goes to the posterior face of the gill in front of 

 the cleft to which it belongs, the other to the anterior face of 

 the gill next behind. In this way all the gill filaments 

 except those on the posterior face of the hyoid and those on 

 the anterior face of the first branchial arch (first and second 

 demibranchs) are supplied. 



215. The glossopharyngeal or ninth nerve (Fig. 22, 

 IX), seen emerging from its foramen, in front of the anterior 

 branchial branch of the vagus : it divides above the first gill 

 cleft and supplies the hyoid half-gill and the anterior half- 

 gill of the first branchial arch [hy, br.i). 



216. The brachial plexus (Fig. 22, br), lying in the 

 depression between the median and lateral ridges of the 

 anterior vertebral plate, and formed by the convergence and 

 subsequent union of the first sixteen or eighteen spinal 

 nerves : the common trunk thus formed turns round the 

 posterior edge of the lateral ridge, and passes outwards 

 behind the propterygium to the pectoral fin. Each spinal 

 nerve arises by two roots, a dorsal (Fig. 11, d.r) and a 

 ventral {v.r), the former having a ganglionic enlargement : 

 the two pass separately through the wall of the neural canal 

 (see §§ 8, 10) and unite outside it in the trunk (/;-) of the 

 nerve. 



XLVIII. Remove carefully the greater part of the 

 membranous labyrinth, cut away the walls of the 

 auditory capsule, and make out 



217. The auditory or eighth nerve (Fig. 22, VIII), 

 entering the capsule at its anterior end through the in- 

 ternal auditory meatus, and passing backwards, sends off 



