THE HEAD AND NECK 1231 



Summary. — The spinal portion of the spinal accessory nerve supplies two 

 muscles, namely, the trapezius and the stemo-cleido-mastoid. The bulbar 

 portion, through its connection with the pneumogastric nerve and its branches, 

 supplies (i) the muscles of the soft palate, except the tensor palati ; {2) the 

 constrictor muscles of the pharynx ; and (3) the intrinsic muscles of the 

 larynx. It also furnishes the inhibitory fibres of the heart, which reach that 

 organ through the cardiac branches of the pneumogastric. 



Hypoglossal Nerve. 



The hypoglossal or twelfth cranial nerve consists at first of two 

 bundles, which pierce the dura mater separately. In passing 

 through the anterior condylar foramen these t%vo bundles unite 

 to form one trunk. After emerging from that foramen the nerve 

 lies deeply under cover of the internal carotid artery and internal 

 jugular vein. It then turns roimd the outer side of the ganglion 

 of the trunk of the pneumogastric, with which it is closely connected, 

 and passes forwards between the internal carotid artery and internal 

 jugular vein. Thereafter it descends to the lower border of the 

 posterior belly of the digastric, at which level it hooks round the 

 occipital artery from without inwards, and crosses in front of the 

 external carotid artery and its lingual branch. In this part of its 

 course the nerve lies in the superior carotid triangle. It next 

 courses forwards above the hyoid bone, passing beneath the tendon 

 of the digastric and the lower part of the stylo-hyoid muscle, and 

 resting on the hyo-glossus. Thereafter it disappears beneath the 

 mylo-hyoid, still resting upon the hyo-glossus, where it is accom- 

 panied by the ranine vein, and lies below the deep part of the 

 submaxillary gland. At the anterior border of the hyo-glossus it 

 is connected with the lingual nerve, and then enters the genio-hyo- 

 glossus. 



Branches — i. Of Communication. — After emerging from the 

 anterior condylar foramen, the hypoglossal nerve communicates 

 with the ganglion of the trunk of the pneumogastric. It then 

 receives a branch from the superior cervical ganglion of the sympa- 

 thetic, and one from the first cervical nerve, or the loop between the 

 first and '=;econd. As it hooks round the occipital artery, it receives 

 the lingual branch of the vagus from the pharyTigeal plexus ; 

 and at the anterior border of the hyo-glossus it is connected with the 

 lingual ner\^e. 



2. Of Distribution. — One or two meningeal branches arise from 

 the nerve in the anterior condylar foramen, which take a recurrent 

 course, and enter the cranial cavity to supply the dura mater in 

 the vicinity of the foramen. 



The descendens cervicis (descendens hypoglossi) nerve has been 

 already described (see Index. 



The thyro-hyoid nerve will be found described on p. 1108. 



The muscular branches are given off from the nerve as it lies upon 

 the hyo-glossus imder cover of the mylo-hyoid. These supply the 

 stylo-glossus, hyo-glossus, genio-hyo-glossus, and genio-hyoid. The 



