DISSECTION OF THE DOG 167 



and lies alongside the cranial cervical sympathetic ganghon. It will be found 

 on the surface of the ventral straight muscle of the head, and has the occipital 

 and internal carotid arteries on its lateral surface. 



The vagus nerve enters the neck by running beneath the wing of the atlas, 

 and, immediately beyond the nodose ganglion, is joined by the sympathetic 

 nerve-cord. The combined nerve has already been examined during the 

 dissection of the neck. 



The following branches leave the portion of the vagus nerve which is now 

 under examination : (1) A small auricular branch (ramus auricularis) leaves 

 either the jugular ganglion or its immediate neighbourhood and enters the 

 facial canal of the temporal bone. (2) Two 'pharyngeal branches (rami pharyngei) : 

 {a) the first arises from the vagus between the jugular and the nodose gangUa, 

 and, traversing the side of the pharynx, crosses the superior laryngeal nerve 

 medially to end in the crico-thyroid muscle of the larynx. Close to its origin 

 it contributes a twig to the second pharyngeal ramus. (6) The second ramus 

 takes its main origin from the nodose ganglion, and is reinforced as just stated. 

 The ramus passes over the surface of the thjnro- and crico-pharyngeal muscles — 

 to which it supplies twigs — joins the recurrent nerve and supplies the thyroid 

 gland. (3) The superior laryngeal nerve (n. laryngeus superior) arises from the 

 nodose ganglion, crosses the thyro-pharyngeal muscle and disappears into an 

 interval between the hyo-pharyngeal, thyro-pharyngeal, and thyro-hyoid 

 muscles. The termination of the nerve in the mucous membrane of the 

 larynx, and its connection with the recurrent nerve, wiU be revealed during 

 the dissection of the larynx. Branches from the superior laryngeal nerve pass 

 to the adjacent sympathetic ganglion, to the first pharyngeal branch of the 

 vagus, and to the hyo-pharyngeal muscle. 



N. ACCBSSOKiTJS. — Like the two preceding nerves, the accessory or eleventh 

 cerebral nerve makes its exit from the cranium by the jugular foramen. The 

 nerve crosses the surface of the ventral straight muscle of the head and then, 

 after supplying the sterno-cephalic muscle, reaches the side of the neck, where 

 it has already received attention. Branches connect it with the nodose 

 plexus of the vagus and the adjacent sympathetic ganglion. 



N. HYPOGLOSSUS. — The disposition, course, and distribution of the hypo- 

 glossal or twelfth cerebral nerve were considered earlier. 



At the present stage of the dissection it is convenient to examine the ventral 

 branch of the first spinal nerve, which runs alongside the vagus and accessory 

 nerves for a short distance. It is connected with the sympathetic and vagus 

 nerves, and also with the descending branch of the hypoglossal nerve. 



Ganglion cbevicale ceaniale. — The more cranial ganghon of the cervical 

 part of the sympathetic nervous system hes by the side of the nodose ganghon 

 of the vagus nerve, where it is crossed by the occipital artery. The ganghon is 

 elongated, fusiform, and greyish in colour, and from its caudal extremity pro- 

 ceeds a nerve-cord which soon becomes almost inseparably joined to the vagus. 



M i 



