166 THE FROG CHAP. 



one of which, the palatine (Fig. 53, VII 1 ), supplies the 

 mucous membrane of the roof of the mouth, and the 

 other, or hyomandibular (VII 2 ), sends branches to the 

 skin and muscles of the lower jaw and to the muscles of 

 the hyoid. It is a mixed nerve. 



The eighth or auditory nerve (Fig. 49, VIII) arises 

 from the medulla just behind the seventh, passes through 

 an aperture in the inner wall of the auditory capsule, 

 and is distributed to the auditory organ or membranous 

 labyrinth (see Figs. 49 and 53). It is the nerve of 

 hearing, and is purely sensory. 



The ninth or glossopharyngeal (Figs. 49 and 53, IX) 

 arises behind the auditory nerve. It sends a branch to 

 join the facial, and supplies the mucous membrane of 

 the tongue and pharynx as well as certain small muscles 

 connected with the hyoid. It is also a mixed nerve. 



The tenth or vagus (Figs. 49 and 53, X) is a large 

 nerve arising in common with the ninth, and dilating, 

 shortly after leaving the skull, into a vagus ganglion. 

 It supplies the larynx (Xlar), the heart (Xcd), the 

 lungs (Xpul), and the stomach (Xgas), and is there- 

 fore often known as the pneumogastric. It has 

 thus an extraordinarily wide distribution, being 

 in fact the only cerebral nerve which supplies parts 

 beyond the head. It is a mixed nerve, and contains 

 many motor fibres, but its branches some of which 

 have to do with the regulation of the heart's contraction 

 and with respiration are better described as efferent 

 and afferent than as motor and sensory : the meaning 

 of these terms will be explained later on. The ninth 

 and tenth nerves leave the skull close together through 

 the aperture noticed in the exoccipital bone. 



The sympathetic nerve (Sy) extends forwards from its 

 junction with the first spinal nerve, joins the vagus, and 

 finally ends anteriorly in the Gasserian ganglion. 



