916 NEUROLOGY 



through the mass of connective tissue which unites the two nerves. As the 

 winds around the occipital artery it gives off a filament to the pharyngeal plexus. 



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 a filament derived from the loop connecting the first and 

 second cervical nerves. 



The communications with the lingual take place near the anterior border of the 

 Hyoglossus by numerous filaments which ascend upon the muscle. 



Branches of Distribution. The branches of distribution of the hypoglossal nerve 

 are: 



Meningeal. Thyrohyoid. 



Descending. Muscular. 



Of these branches, the meningeal, descending, thyrohyoid, and the muscular 

 twig to the Geniohyoideus, are probably derived mainly from the branch which 

 passes from the loop between the first and second cervical to join the hypoglossal 

 (Fig. 795). 



Meningeal Branches (dural branches}. As the hypoglossal nerve passes through 

 the hypoglossal canal it gives off, according to Luschka, several filaments to the 

 dura mater in the posterior fossa of the skull. 



The Descending Ramus (ramus descendens; descendens hypoglossi), long and slender, 

 quits the hypoglossal where it turns around the occipital artery and descends in 

 front of or in the sheath of the carotid vessels; it gives a branch to the superior 

 belly of the Omohyoideus, and then joins the communicantes cervicales from the 

 second and third cervical nerves; just below the middle of the neck, to form a loop, 

 the ansa hypoglossi. From the convexity of this loop branches pass to supply 

 the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omo- 

 hyoideus. According to Arnold, another filament descends in front of the vessels 

 into the thorax, and joins the cardiac a.nd phrenic nerves. 



The Thyrohyoid Branch (ramus thyreohyoideus} arises from the hypoglossal near 

 the posterior border of the hyoglossus; it runs obliquely across the greater cornu 

 of the hyoid bone, and supplies the Thyreohyoideus muscle. 



The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Genio- 

 hyoideus, and Genioglossus. At the under surface of the tongue numerous slender 

 branches pass upward into the substance of the organ to supply its intrinsic muscles. 



THE SPINAL NERVES (NERVI SPINALES). 



The spinal nerves spring from the medulla spinalis, and are transmitted through 

 the intervertebral foramina. They number thirty-one pairs, which are grouped 

 as follows: Cervical, 8; Thoracic, 12; Lumbar, 5; Sacral, 5; Coccygeal, 1. 



The first cervical nerve emerges from the vertebral canal between the occipital 

 bone and the atlas, and is therefore called the suboccipital nerve ; the eighth issues 

 between the seventh cervical and first thoracic vertebra?. 



Nerve Roots. Each nerve is attached to the medulla spinalis by two roots, 

 an anterior or ventral, and a posterior or dorsal, the latter being characterized by 

 the presence of a ganglion, the spinal ganglion. 



The Anterior Root (radix anterior; ventral root) emerges from the anterior surface 

 of the medulla spinalis as a number of rootlets or filaments (fila radicularia) , 

 which coalesce to form two bundles near the intervertebral foramen. 



The Posterior Root (radix posterior; dorsal root) is larger .than the anterior owing 

 to the greater size and number of its rootlets; these are attached along the posterp- 

 lateral furrow of the medulla spinalis and unite to form two bundles which join 

 the spinal ganglion. The posterior root of the first cervical nerve is exceptional 

 in that it is smaller than the anterior; it is occasionally wanting. 





