HEAD AND NECK OF THE HORSE 67 



diverticulum of the auditory tube, crosses the external carotid artery 

 medially, and divides into two branches. The upper of these supplies 

 the constrictor muscles and the mucous membrane of the pharynx. The 

 lower branch ramifies in connection with the pliaryngeal plexus (plexus 

 pharyngeus). This plexus is formed by filaments from the glosso- 

 pharyngeal, accessory, hypoglossal, digastric, cranial laryngeal, first 

 cervical and sympathetic nerves ; and from it slender nerves pass to the 

 diverticulum, the soft palate, the wall of the pharynx and the 

 commencement of the oesophagus. 



(2) N. laryngeus cranicdis. — The cranial laryngeal nerve crosses 

 the medial face of the external carotid artery, runs over the surface of 

 the crico- and thyro-pharyngeal muscles, and pierces a cleft between 

 the anterior cornu and the lamina of thyroid cartilage to end in the 

 mucous membrane of the larynx, the ventral wall of the pharynx and 

 the commencement of the oesophagus. The terminal part of the nerve 

 will be examined in connection with the larynx. 



At the origin of the cranial laryngeal nerve, the vagus is flattened 

 and widened to a variable degree. Sometimes an elongated grey 

 enlargement can be determined. This is the homologue of the nodose 

 ganglion (ganglion nodosum) of other mammals. 



N. ACCESSORius. — The accessory or eleventh cerebral nerve leaves 

 the cranium by the jugular foramen along with the vagus, with which 

 it is included in a common sheath for a distance that varies in different 

 subjects. After separating from the vagus, the accessory, crossing the 

 medial aspect of the submaxillary gland and the occipital artery, passes 

 backwards into the fossa atlantis, where it divides into dorsal and 

 ventral branches. The dorsal branch is joined by a part of the second 

 cervical nerve, and enters the neck between the brachio -cephalic and 

 splenius muscles. Its subsequent course and termination were con- 

 sidered during the dissection of the neck (page 17). The termination 

 of the ventral branch in the sterno-cephalic muscle has also been noted 

 (page 2). 



N. HYPOGLOSSUS.— The twelfth cerebral or hypoglossal nerve leaves 

 the cranium by the hypoglossal foramen. Passing obliquely downwards 

 and forwards, it runs between the vagus and accessory nerves at their 

 angle of divergence. Its course on the lateral wall of the diverticulum 

 of the auditory tube and onwards to the tongue has been previously 

 revealed (page 64). 



N. CERViCALis PRIMUS.— The ventral branch of the first cervical 

 nerve enters the fossa atlantis by the foramen alare. Branches are 



