THE NERVOUS SYSTEM OF THE DOG 729 



and ramifies on the lateral surface of the face. The inferior alveolar nerve arises 

 by a common trunk with the mylo-hyoid; it gives off dental branches and term- 

 inates in mental and inferior labial branches. The lingual nerve supplies vaso- 

 dilator and excito-secretory filaments to the submaxillary and sublingual salivary 

 glantls; these fibers are derived from the chorda tympani. 



The facial nerve divides near the j^osterior border of the jaw into four branches. 

 The upper Inanch is the auriculo-palpebral nerve, which divides after a very short 

 course into anterior auricular and zygomatic branches. The latter curves upward 

 and forward across the zygomatic arch toward the eye, and divides into branches 

 which sui)ply the eyelitls and nasal region and concur with the frontal and lacrimal 

 nerves in forming the anterior auricular plexus. The superior buccal nerve ac- 

 com[mnies the jjarotid duct across the masseter. The inferior buccal nerve runs 

 forward along the lower border of the masseter and the mandible. The two nerves 

 ramify on the cheek and anastomose with each other and the infraorbital nerves 

 to form a i)l('xus from which branclu^s go to the muscles of the lips and nostrils. 

 The cervical branch runs downward and backward over the submaxillary gland 

 and ramifies in the cervical panniculus; it communicates with the inferior buccal 

 nerve and sends twigs to the ])arotido-auricularis muscle and the submaxillary 

 space. 



The vagus Ijears a jugular ganglion and a ganglion nodosum. The latter is 

 situated near the superior cervical ganglion on the rectus capitis anterior major 

 and dorsal to the carotid artery; it is fusiform and may be about half an inch (ca. 

 1 to 1.5 cm.) long in a large dog. In its course in the neck the nerve is inclosed with 

 the sym])at luetic trunk in a connnon sheath and is related ventrally to the common 

 carotid artery. The formation of dorsal and ventral oesophageal trunks by the 

 union of the dorsal and ventral divisions of the two nerves takes place at the hiatus 

 cesophageus. The dorsal trunk concurs with branches of the solar plexus in forming 

 the posterior gastric plexus on the visceral surface of the stomach. The ventral 

 trunk ramifies on the parietal surface of the stomach, forming the anterior gastric 

 plexus, from which a consideral)le branch passes along the lesser curvature to the 

 pylorus. Some special features of the collateral branches are: Two pharyngeal 

 branches are present. The superior pharyngeal branch arises from the vagus 

 above the ganglion nodosum. It passes under the deep face of the carotid artery 

 and descends on the lateral surface of the pharynx to end in the crico-thyroid muscle. 

 It furnishes a root of the inferior pharyngeal branch, and communicates with the 

 pharyngeal branch of the ninth and with the superior laryngeal and hypoglossal 

 nerves. The inferior pharyngeal branch is formed by the union of roots derived 

 from the superior pharyngeal nerve and the ganglion nodosum, together with fila- 

 ments from the superior cervical ganglion. It crosses the side of the pharynx 

 behind the superior pharyngeal and ramifies on the posterior constrictor of the 

 pharynx and the origin of the oesophagus. It contributes filaments to the pharyn- 

 geal plexus, communicates with the recurrent nerve, and supplies twigs to the thy- 

 roid gland. The pharyngeal plexus is formed on the lateral surface of the pharynx 

 by branches of the pharyngeal nerves and the communications above described; 

 branches from it innervate the muscles and mucous membrane of the pharynx. 

 The superior laryngeal nerve arises from the ganglion nodosum and descends over 

 the side of the pharynx, crossing beneath the carotid artery and the superior laryn- 

 geal nerve. It passes through the thyroid notch and ramifies in the mucous mem- 

 brane of the larynx. It communicates with the superior cervical ganglion and the 

 superior pharyngeal branch of the vagus, and gives twigs to the hyo-pharyngeus 

 muscle. Immediately after its entrance into the larynx it gives off a large branch 

 which, instead of uniting with the recurrent as in the other animals, has a peculiar 

 arrangement. It runs back near the dorsal border of the thyroid cartilage, gives a 

 branch to the crico-arytenoideus posterior as it passes over that muscle, and con- 



