198 THE ANATOMY OF THE HORSE. 



muscles ; and it here crosses to the inner side of the external carotid 

 artery. Keachiug the pharynx, it continues to descend either close 

 behind the posterior edge of the great cornu or under cover of it ; and 

 here it is crossed by tlie pharyngeal artery, which may pass either over 

 or under it. It next passes within the articulation of the great and 

 small cornua to reach the root of the tongue, where its terminal branches 

 will be seen at a later stage. It gives off the following branches, the 

 first of which will not now be seen : — 



1. The Nerve of Jacobson, given off from Andersch's ganglion — a 

 minute ganglion placed on the nerve where it issues from the cranium. 

 Jacobson's nerve penetrates between the petrous and temporal parts of 

 the temporal bone and enters the tympanum, to the mucous membrane 

 of which it is distributed. 



2. Branches of communication with the superior cervical ganglion of 

 the sympathetic. 



3. A Branch to the Carotid Plexus. 



4. A Pharyngeal Branch, which is given off at or near the point where 

 the nerve crosses the external carotid. It is as large as the glossal 

 continuation of the trunlc, and it passes on to the wall of the pharynx, 

 behind the stylo-pharyugeus muscle. 



5. A Branch to the Stylo-pharyngeiis muscle. — This may be detached 

 either before or after the preceding branch. It enters the outer side of 

 the muscle. 



The 12th Cranial Nerve, called also the Hypoglossal (Plate 32), 

 leaves the cranium by the condyloid foramen. It passes through the 

 angle of separation of the 10th and 11th nerves, and descends on the 

 guttural pouch, ci'ossing to the outer side of the external carotid at or 

 near the origin of the submaxillaiy artery. It next crosses the pharynx 

 in company with the submaxillary artery, and passes under the angle 

 formed by that vessel and its lingual branch. It is continued to the 

 muscles of the tongue. Where the nerve lies on the guttural pouch it 

 is covered by the stylo-maxillaris, digastric, and stylo-hyoid muscles, and 

 below that point it is covered by tlie internal pterygoid muscle. 



On the pharynx the hypoglossal is joined by a considerable twig from 

 the inferior piimary branch of the 1st spinal nerve. On the guttural 

 pouch it constantly communicates with the superior cervical ganglion of 

 the sympatlietic. It has no other branches until it reaches the tongue. 



The 10th Cranial Nerve, also termed the Vagus or Pneumogastric 

 (Plate 32), issues from the cranium by the extreme posterior part of 

 the foramen lacerum basis cranii. For about one inch and a half of its 

 course it forms a common cord with the 11th nerve, which issues at the 

 same point. The two nerves then separate (the 12th nerve passing 

 through the angle), and the vagus passes downwards and backwards on 

 the guttural pouch. It passes over the internal carotid artery, and 



