COMPARATIVE ANATOMY OF THE NERVOUS SYSTEM 343 



passes to the dorsal side of the mylohyoid muscle, which may be cut, and inner- 

 vates the muscles of the tongue. 



About halfway between the descending branch and main part of the hypo- 

 glossal nerve, but deeper dorsally and passing to the dorsal side of the carotid 

 artery, is situated the superior laryngeal branch of the vagus nerve. It runs 

 obliquely caudad to the larynx which it penetrates, passing through the fibers 

 of the thyrohyoid muscle. 



Follow the vagus and sympathetic once more. At the place where the 

 descending branch of the hypoglossal crosses them the two separate in the cat. 

 Shortly anterior to this the vagus in both animals presents an elongated swelling, 

 the nodosal ganglion. At about the same level, but more medial in position, the 

 sympathetic trunk enters the superior cervical ganglion of the sympathetic, an 

 elongated pinkish body. The two ganglia lie just posterior to the hypoglossal 

 as it curves forward into the tongue. 



The hypoglossal, the accessory, the vagus, and the sympathetic are all 

 involved in a plexus in which the first cervical nerves also take part. 



c) The ninth or glossopharyngeal nerve: This lies very close to the main 

 part of the hypoglossal nerve but more deeply dorsal. Dissect directly internal 

 to the hypoglossal where it curves anteriorly to the tongue. The glossopharyngeal 

 is a smaller nerve lying dorsal to the hypoglossal along the sides of the pharynx 

 anterior to the larynx. It is situated between the two horns of the hyoid. It 

 divides into two branches: a smaller pharyngeal branch passing medially into 

 the pharynx and a main lingual branch which enters the tongue. The former 

 is a motor nerve to muscles of the pharynx, while the lingual branch is a nerve 

 of taste. 



Follow the nerves thus far described toward the point where they emerge 

 from the skull. They are found to converge to a point to the medial side of 

 the tympanic bulla. Here the ninth, tenth, and eleventh nerves emerge from the 

 brain through the jugular foramen, located on the medial side of the bulla. 

 The twelfth nerve emerges near the others through the hypoglossal foramen 

 (consisting of several openings in the rabbit). 



d) The seventh or facial nerve: The main part of this nerve is very super- 

 ficial in position. It emerges at the posterior end of the masseter muscle at the 

 base of the ear, in a sort of depression. On carefully searching in this region 

 it will be found as a stout white band, in contact with the main part of the external 

 carotid artery. At this place the facial gives off a branch to the posterior part 

 of the digastric muscle, and the posterior auricular nerve to the pinna. (The 

 large nerve to the pinna which may be noticed dorsal to this branch of the facial 

 is the great auricular nerve originating in the cervical plexus.) The facial then 

 proceeds forward, branching over the external surface of the masseter muscle, 

 and passes to the lips and region of the eye. It supplies the various parts of 

 the platysma muscle, which it may be recalled is a dermal muscle of the head 



