NINTH OR HYPOGLOSSAL NERYE. 545 



Branches of tins nerve communicate with the 



Pneumogastric. First and second cervical nerves. 



Sympathetic. Gustatory. 



The communication with the pneumogastric takes place close to the exit of the 

 nerve from the skull, numerous filaments passing between the hypoglossal and 

 second ganglion of the pneumogastric, or both being united so as to form one mass. 



^The communication with the sympathetic takes place opposite the atlas, by 

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

 it is joined by a filament with the loop connecting the first two cervical nerves. 



The communication with the 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 



Descendens noni. Thyro-hyoid. 



Muscular. 



The Descendens noni is a long slender branch, which quits the hypoglossal 

 where it turns round the occipital artery. It descends obliquely across the sheath 

 of the carotid vessels, and joins just below the middle of the neck, to form a loop 

 with the communicating branches from the second and third cervical nerves. From 

 the convexity of this loop, branches pass forwards to supply the Sterno-hyoid, 

 Sterno-thyroid, and both bellies of the Omo-hyoid. According to Arnold, another 

 filament descends in front of the vessels into the chest, which joins the cardiac 

 and phrenic nerves. The descendens noni is occasionally contained in the sheath 

 of the carotid vessels, being sometimes placed over and sometimes beneath the 

 internal jugular vein. 



The Tkyro-hyoid is a small branch, arising from the hypoglossal near the pos- 

 terior border of the Hyo-glossus ; it passes obliquely across the great cornu of the 

 hyoid bone, and supplies the Thyro-hyoid muscle. 



The Muscular branches are distributed to the Stylo-glossus, Hyo-glossus, 

 Genio-hyoid, and Genio-hyo-glossus muscles. At the under surface of the tongue, 

 numerous slender branches pass upwards into the substance of the organ. 



3. NERVES OF COMMON SENSATION. 

 FIFTH NERVE. 



The FIFTH NERVE (trifacial, trigeminus) is the largest cranial nerve, and resem- 

 bles a spinal nerve, in its origin by two roots, and in the existence of a ganglion 

 on its posterior root. The functions of this nerve are various. It is a nerve of 

 special sense, of common sensation, and of motion. It is the great sensitive nerve 

 of the head and face, the motor nerve of the muscles of mastication (except the 

 Buccinator), and its lingual branch is one of the nerves of the special sense of 

 taste. It arises by two roots, a posterior larger or sensory, and an anterior smaller 

 or motor root. Its superficial origin is from the side of the pons Varolii, a little 

 nearer to its upper than its lower border. The smaller root consists of three or 

 four bundles ; in the larger, the bundles are more numerous, varying in number 

 from seventy to a hundred; the two roots are separated from one another by a 

 few of the transverse fibres of the pons. The deep origin of the larger or sensory 

 root may be traced between the transverse fibres of the pons Varolii to the lateral 

 tract of the medulla oblongata, immediately behind the olivary body. According 

 to some anatomists, it is connected with the gray nucleus at the back part of the 

 medulla, between the fasciculi teretes and restiform columns. By others, it is 

 said to be continuous with the fasciculi teretes and lateral column of the cord ; 

 and, according to Foville, some of its fibres are connected with the transverse 

 fibres of the pons ; whilst others enter the cerebellum, spreading out on the sur- 

 face of its middle peduncle. The motor root has been traced by Bell and Retziu.s 

 to be connected with the pyramidal body. The two roots of the nerve pass for- 

 wards through an oval opening in the dura mater, at the apex, of the petrous 

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