CRANIAL NERVES. 175 
IX. The Glossopharyngeal, the first of the post-otic nerves, has its 
typical development in the branchiate vertebrates. Its roots, both 
motor and sensory, pass into the petrosal ganglion, beyond which a 
dorsal famus is given off to the top of the head, while the main trunk, 
passing outward and backward, leaves the skull, either by its own fora- 
men (most branchiates) or together with the tenth nerve (anura and 
amniotes). It divides, just above the first gill cleft, into pre- and post- 
trematic nerves, which run in the anterior and posterior walls of the 
cleft to the ventral wall of the pharynx, the pretrematic giving off a 
nerve to the mucous membrane of the palate. Ninth and tenth nerves 
Fic. 173.—Diagram of ninth (glossopharyngeal) and tenth (vagus) nerves of a shark; 
for components see fig. 170. d, dorsal ramus; g, gastric nerve; #, to heart; 7, Jacobson’s 
commissure; /, lateralis nerve; /g, lateralis ganglion; po, pr, post- and pretrematic branches; 
sp, spiracle; st, to supratemporal lateral line organs. 
are usually closely associated (their ganglia may fuse), while ninth and 
fifth are frequently connected by Jacobson’s commissure and the pala- 
tine branch may connect with the geniculate ganglion. The glos-- 
sopharyngeal may contain three kinds of components, the somatic 
motor fibres being absent because of the failure of themyotomic muscles 
to develop. The general cutaneous is usually represented by the dorsal 
ramus alone, but in Petromyzon its fibres reach the ventral skin through 
the post-trematic nerve. The visceral sensory fibres reach the taste 
organs by way of the pharyngeal and lingual nerves, while the visceral 
motor elements go to the muscles of the gill region by way of the post- 
trematic ramus. 
X. The Vagus is a complex of nerves, each similar to the ninth, 
with the addition, in the branchiates, of lateralis components, and sup- 
plying in them the remaining gill clefts. Numerous rootlets pass from 
