HYPOGLOSSAL NERVE. 



627 



enclose an irregularly shiped space. From this interlacement of the nerves, 

 filaments are continued backwards to the posterior belly of the omo-hyoid, 

 and downwards to the sterno-hyoid and stern o- thyroid muscles. Occasionally 

 a filament is continued to the chest, where it joins the cardiac and phrenic 

 nerves. 



Fig 419 





Fig. 419. VIEW OF THE DISTRIBUTION OP THK SPINAL ACCESSORY AND HrpoaiossAi, 

 NERVES (from Sappey after Hirschfeld and Leveille). ^ 



1, lingual nerve ; 2, pneumo-gasiric nerve ; 3, superior laryngeal (represented too large) ; 

 4, external laryngeal branch ; 5, spinal accessory ; 6, second cervical ; 7, third ; 8, 

 fourth ; 9, origin of the phrenic nerve; 10, origin of the branch to the subclavius muscle ; 

 11, anterior thoracic nerves ; 12, hypoglossal nerve ; 13, its descending branch ; 14, com- 

 municating branch from the cervical nerves; 15, 16, 18, 19, descending branches from 

 the plexiform union of these nerves to the sterno-hyoid, sterno-thyroid, and omo-hyoid 

 muscles ; 17, branch from the descendens noni to the upper belly of the omo-hyoid 

 muscle ; 20, branch from the hypoglossal nerve to the tbyro-hyoid muscle ; 21, communi- 

 cating twigs from the hypoglossal to the lingual nerve ; 22, terminal distribution of the 

 hypoglossal to the muscles of the tongue. 



It is not uncommon to find the descending branch of the ninth nerve within the 

 sheath of the large cervical vessels, and in such cases it is placed either over or under 

 the vein. This nerve in some cases appears to be derived either altogether from the 

 pneumo-gastric, or from both the pneumo-gastric and hypoglossal nerves. There is 

 every reason, however, to believe that these varieties in origin are only apparent, 

 arising from the temporary adhesion of the filaments of this branch to those of the 



