698 



THE NEEVOUS SYSTEM. 



cervical nerves (Fig. 613). A trunk from the loop joins the hypoglossal just beyond 

 its exit from the skull. One fine branch from this trunk passes upwards along 

 the hypoglossal nerve to the cranium (meningeal branch'). The main part of the 

 trunk accompanies the hypoglossal and separates from it to form successively three 

 nerves the descendens hypoglossi, and the nerves to the thyreo-hyoid and genio-hyoid 

 muscles. The portion of the nerve which remains accompanies the hypoglossal to 

 the muscles of the tongue. It is probable that no part of the hypoglossal nerve 

 itself is concerned in the formation of these three branches. The descending 

 branch of the hypoglossal descends in front of the internal and common carotid 



C2 



SCENOINO CERVICAL 



FIG. 613. THE MUSCLES OP THE HYOID BONE AND STYLOID PROCESS, AND THE EXTRINSIC MUSCLES OF 



THE TONGUE, WITH THEIR NERVES. 



arteries, and is joined in the anterior triangle of the neck by the descending 

 cervical nerve, to form the ansa hypoglossi, from which the infra-hyoid muscles 

 are innervated. . (The descending branch of the hypoglossal, in some cases, arises 

 from the vagus nerve. ^ 



Muscular Branches. The muscles supplied by the medial branches of the 

 plexus are the prevertebral muscles, the genio-hyoid and the infra-hyoid muscles, 

 and the diaphragm. 



(a) Prevertebral Muscles. 1. From the loop between the first and second 

 cervical nerves a small branch arises, for the surmlv of the rectus capitis lateralis, 



