468 NERVOUS SYSTEM. 



yond a certain point. The most satisfactory account has 

 been published by Meckel.* 



SECT. VIII. NERVUS HYPOGLOSSUS. 



The Hypoglossal Nerve, (Nervus Hypoglossus, LingualisJ) 

 having arisen from the medulla oblongata, and escaped from 

 the cranium through the anterior condyloid foramen, adheres 

 closely for an inch to the prfeumogastric nerve. It descends 

 between the external carotid artery and the internal jugular 

 vein, the latter being behind the other; and then winds over 

 the carotid, externally, just below the origin of the occipital ar- 

 tery. It is there covered by the posterior belly of the digas- 

 tricus and by the stylo-hyoideus. It then passes forwards be- 

 neath the external jugular vein, and lower down somewhat than 

 the tendon of the digastric muscle, and, finally, ascends to the 

 tongue, being covered or concealed by the mylo-hyoideus mus- 

 cle. The nerve in this course, from the external carotid to the 

 tongue, forms a remarkable curve, the convexity of which is 

 downwards. 



The Hypoglossal, while adhering to the pneumo-gastric, com- 

 monly leaves a few filaments with it. As it crosses the ex- 

 ternal carotid, it detaches a large branch, the Ramus Descen- 

 dens Noni, which goes down the neck, along the sheath of 

 the carotid artery and the internal jugular vein, in front of the 

 latter. 



The ramus descendens has been beautifully figured by Scar- 

 pa, in his Plates of the Nerves. According to him, when it 

 has got about half way down the neck, but still resting on the 

 sheath of the vessels, it detaches, in front, two filaments, which, 

 after the course of an inch forwards, unite, and then separate 

 again to be distributed to the upper ends of the omo-hyoid and 

 sterno-hyoid muscles. The descendens noni then forms, an 

 inch lower down, a small gangliform plexus, resting upon the 

 sheath of the great vessels of the neck, under the omo-hyoid 

 muscle. This plexus is joined by two fasciculi, which descend 

 from the first and second cervical nerves, and from it pro- 



* J. F. Meckel, de Nervis Faciei, Mem. de 1'Acad. des S. de Berlin, 1751, Cal- 

 dani, Tab. 247. 



