HYPOCLOSSAL XERVE 775 



Branches. — Tlie meningeal branch ( Lusclika) is given off by the hypoglossal 

 as it is traversing the anterior condyloid foramen, and takes a recurrent course into 

 the cranial cavity, where it is distributed to the dura mater. It is probably derived 

 from the connnunicating branches of the pneumogastric or from the first cervical 

 nerve. 



The remaining lirnnclics of tlic liyjioglossal may be classified into branches of 

 the cervical plexus which are simply adiierent for the time being to the cranial 

 nerve, and true hypoglossal branches; the latter are exclusively distributed to the 

 muscles of the tongue and the genio-hyoid. 



The BRANCHES DERIVED FROM THE CERVICAL PLEXUS are the descendens 

 hyjjoglossi, and the muscular twig to the thyro-hyoid muscle. 



The descendens hypoglossi parts company with the hypoglossal at the point 

 where the latter hooks round the occipital artery. It runs downwards and slightly 

 inwards on the sheath of the great vessels (occasionally within the sheath), and is 

 joined at a variable level by the communicantes hypoglossi from the second and 

 third cervical nerves, forming a loop, the ansa hypoglossi. The ansa hypoglossi 

 may be placed at any level from a point immediately below the occipital artery to 

 al)out an inch and a half aVjove the sternum. A twig to the anterior belly of the 

 omo-hyoid arises from the descendens hypoglossi in the upper part of its course. 

 The nerves Avhich supply the sterno-hj^oid, sterno-thyroid, and posterior belly of 

 the omo-hyoid are given off by the ansa hypoglossi. Twigs from the first two 

 nerves pass in the muscles behind the manubrium stemi and in rare cases com- 

 nnmicate with the phrenic within the thorax. The nerve to the posterior belly of 

 the omo-hyoid runs in a loop of the cervical fascia below the central tendon of 

 the muscle. 



The nerve to the thyro-hyoid is given off near the tip of the great cornu 

 of the hyoid bone, and runs oblicpiely downwards and inwards to reach the 

 nuiscle. 



The TRUE HYPOGLOSSAL BRANCHES supply the stylo-glossus, hyo-glossus, 

 genio-hyo-glossus, the genio-hyoid, and the intrinsic muscular fibres of t he 

 tongue. *-«-,...«..-«^.-. - - • "'"'■'" 



Tlie nerve to the stylo-glossus is given off near the oviter border of the 

 hyo-glossus. It pierces the stylo-glossus, and its fibres pursue a more or less 

 recurrent cour.se within the muscle. 



The nerves to the hyo-glossus are several tAvigs Avhich are supplied to the 

 muscle as the hypoglossal nerve crosses it. 



The nerves to the genio-hyo-glossus and genio-hyoid arise under cover 

 of the mylo-hyoid in common with the terminal 1)ranches to the intrinsic muscles 

 of the tongue. They communicate freely with branches of the lingual, forming 

 long loops which lie on the hyo-glossus muscle. From these loops twigs pass into 

 the genio-hyo-glossus and into the muscular substance of the tongue. 



