FIFTH. 615 



Branches of this 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 

 the ninth is joined by a filament derived from 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 cervi- 

 cal 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 occasion- 

 ally contained in the sheath of the carotid vessels, being sometimes placed over 

 and sometimes beneath the internal jugular vein. 



The tliyro-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. 



FIFTH NERVE. 



The Fifth Nerve (trifacial, trigeminus) is the largest cranial nerve, and re- 

 sembles 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 masti- 

 cation, 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 Varplii, a little 

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

 or four bundles ; in the larger, the bundles are more numerous, varying in num- 

 ber 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 Yarolii 

 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 col- 

 umns. 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 cere- 

 bellum, spreading out on the surface of its middle peduncle. The motor root 

 has been traced by Bell and Retzius to be connected with the pyramidal body. 

 The two roots of the nerve pass forwards through an oval opening in the dura 



