824 



THE NERVOUS SYSTEM. 



Communication between 1st and 2d 

 Cervical Nerves and Hypoglossal 



glossi) in the floor of the fourth ventricle, and extending downward into the 

 closed portion of the medulla. The filaments of this nerve are collected into two 



bundles which perforate the dura 

 mater separately, opposite the an- 

 terior condyloid foramen, and 

 unite together after their passage 

 through it. In those cases in 

 which the anterior condyloid for- 

 amen in the occipital bone is 

 double these two portions of the 

 nerve are separated by the small 

 piece of bone which divides the 

 foramen. The nerve descends al- 

 most vertically to a point corre- 

 sponding with the angle of the 

 jaw. It is at first deeply seated 

 beneath the internal carotid artery 

 and internal jugular vein, and in- 

 timately connected with the pneu- 

 mogastric nerve ; it then passes 

 forward between the vein and 

 artery, and lower down in the 

 neck becomes superficial below 

 the Digastric muscle. The nerve 

 then loops round the occipital 

 artery, the sterno-mastoid branch 

 of which hooks over the nerve, 

 and crosses the external carotid 

 and its lingual branch below the 

 tendon of the Digastric muscle. 



It then passes beneath the tendon of the digastric, the stylo-hyoid, and the Mylo- 

 hyoid muscles, lying on the Hyo-glossus, accompanied by the ranine vein, and 

 communicates at the anterior border of the latter muscle with the lingual (gusta- 

 tory) nerve ; it is then continued forward in the fibres of the Genio-hyo-glossus 

 muscle as far as the tip of the tongue, distributing branches to its substance. 

 The branches of communication are with the 



Infra-hyoid Muscles 



FIG. 493. Plan of communicantes and descendens hypo 

 i nerves. 



Pneumogastric. 

 Sympathetic. 



First and Second Cervical Nerves. 

 Lingual (gustatory). 



The first mentioned takes place close to the exit of the nerve from the skull, 

 numerous filaments passing between the hypoglossal and lower ganglion of the 

 pneumogastric through the mass of connective tissue which here unites the two 

 nerves. It also communicates with the pharyngeal plexus by a minute filament 

 as it winds round the occipital artery (lingual branch, see page 821). 



The communication with the sympathetic takes place opposite the atlas by 

 branches derived from the superior cervical ganglion, and in the same situation 

 the nerve is joined by filaments derived from the loop connecting the first two 

 cervical nerves. 



The communication with the lingual (gustatory) takes place near the anterior 

 border of the Hyo-glossus muscle by numerous filaments which ascend upon it. 



The branches of distribution are the 



Meningeal. 

 Descendens hypoglossi. 



Thyro-hyoid. 

 Muscular. 



Meningeal Branches. As the hypoglossal nerve passes through the anterior 



