194 THE ANATOMY OF THE HORSE. 



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

 it is covered by the stylo-maxiUaris, digastric, and stylo-hyoid muscles, 

 and below that point it is covered by the internal pterygoid muscle. 



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

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

 pouch it constantly communicates with the superior cervical ganglion of 

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



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

 (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 parsing 

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

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

 under the occipital ; and above the first part of the trachea it meets the 

 cervical cord of the sympathetic, the two nerves then uniting to form a 

 common cord, which applies itself to the upper side of the common 

 carotid artery, and descends with it in the neck. Between the foramen 

 lacerum and the point where the nerve joins the sympathetic, it detaches 

 the following branches : — 



1. Branches of Communication with the superior cervical ganglion. 



2. A Pharyngeal Branch is detached near the point where the vagus 

 passes under the occipital artery. It passes to the inner side of the 

 external carotid artery, and reaches the pharynx. There it unites with 

 the sympathetic and the pharyngeal branch of the 9th, forming a plexus 

 from which branches pass to the constrictors and mucous membrane of 

 the pharynx, and to the first part of the oesophagus. 



3. The Superior Laryngeal Nerve is given off near the termination of 

 the common carotid artery ; and crossing beneath the external carotid 

 or the termination of the common carotid, it passes over the pharynx to 

 penetrate the thyroid cartilage at the anterior edge of the thyro- 

 pharyngeus muscle. Within the larynx, as will afterwards be learned, it 

 is distributed to the mucous membrane ; and also gives branches to the 

 pharynx, oesophagus, and root of the tongue. Near its origin it detaches 

 an external laryngeal branch, which passes to the crico-thyroid and crico- 

 pharyngeus muscles. 



The trunk of the vagus is sometimes distinctly gangliform at the 

 point of detachment of its superior laryngeal branch. This is the 

 ganglion of the trunk of human anatomy. 



The 1 1th Cranial Nerve, called also the Spinal Accessory Nerve, 

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

 lacerum, in company with the vagus. For the space of about one inch 

 and a half it forms a common cord with that nerve. It then parts 

 company with the vagus, and passes backwards at the edge of the rectus 



