780 THE NERVOUS SYSTEM. 



parotidei). (3) A twig for the supply of the skin of the external acoustic meatus 

 and membrana tympani (n. meatus auditor!! extern! et ramus membranae tympani). 

 (4) Branches to the superior half of the auricle on its lateral aspect. (5) Terminal 

 branches to the skin of the temple and scalp (ram! temporales superficiales). 



It has the -following communications with other nerves : (1) Important communica- 

 tions are effected by the roots of the nerve, which are separately joined by small branches 

 from the otic ganglion. (2) The parotid branches of the nerve are connected with branches 

 of the facial nerve in the substance of the gland (rami anastomotici c. nervo faciali). 

 (3) The temporal branch of the nerve is in communication superficially with the temporal 

 branches of the facial nerve. 



N. Lingualis. The lingual nerve is the smaller of the two terminal branches 

 of the posterior division of the mandibular trunk. It proceeds downwards in front 

 of the inferior alveolar nerve, medial to- the external pterygoid muscle, to its inferior 

 border. After passing between the internal pterygoid muscle and the ramus of 

 the mandible, it crosses beneath the mucous membrane of the floor of the mouth 

 in the interval between the mylo-hyoid and hyoglossus muscles and beneath the 

 duct of the submaxillary gland. It sweeps forwards and medially to the side of 

 the tongue, to the mucous membrane over the anterior two-thirds of which it is 

 distributed. 



Two nerves communicate with the lingual nerve in its course to the tongue : 



(1) The chorda tympani branch of the facial nerve joins it medial to the external 

 pterygoid muscle, and is incorporated with it in its distribution to the tongue. 



(2) The hypoglossal nerve forms larger or smaller loops of communication with 

 the lingual nerve as they course forwards together over the hyoglossus muscle (rami 

 anastomotici cum nervo hypoglosso). 



Besides supplying the aforesaid branches to the mucous membrane over the sides 

 and dorsum of the tongue in its anterior two- thirds, the lingual nerve supplies the 

 mucous membrane of the side wall and floor of the mouth. It also assists, along 

 with the chorda tympani nerve, in forming the roots of the submaxillary ganglion. 



Ganglion Submaxillare. The submaxillary ganglion is a minute reddish 

 ganglion placed on the hyoglossus muscle, between the lingual nerve and the duct 

 of the submaxillary gland. It is suspended from the former by two trunks, con- 

 sisting for the most part of fibres of the lingual and chorda tympani nerves, which 

 at that point become separated from the lingual nerve and incorporated with the 

 ganglion. The roots of the ganglion are (1) an afferent root, derived from the 

 lingual nerve ; (2) an efferent root, derived from the chorda tympani ; and (3) a 

 sympathetic root, from the sympathetic plexus upon the external maxillary artery. 



The branches from the ganglion are distributed to the submaxillary gland and 

 duct (rami submaxillares), and by fibres which become reunited with the trunk of 

 the lingual nerve, to the sublingual gland. 



N. Alveolaris Inferior. The inferior alveolar nerve (O.T. inferior dental) 

 is larger than the lingual nerve. It passes from beneath the inferior border of the 

 external pterygoid muscle to reach the interval between the ramus of the man- 

 dible and the spheno- mandibular ligament. Entering the mandibular canal 

 through the mandibular foramen, it traverses the substance of the ramus and body 

 of the mandible, distributing branches to the teeth in its course. A fine plexus is 

 formed by the dental branches before they finally supply the teeth. 



Branches and Communications. (1) N. Mylohyoideus. The mylo-hyoid nerve is 

 a small branch arising just before the inferior alveolar nerve passes through the 

 mandibular foramen. Grooving the ramus in its course, it descends into the 

 submaxillary triangle on the superficial aspect of the mylo-hyoid muscle. Concealed 

 in this situation by the submaxillary gland and the external maxillary artery, it 

 is distributed to the mylo-hyoid muscle and the anterior belly of the digastric muscle. 

 (2) N. Mentalis. The mental branch of the inferior alveolar nerve is a trunk of con- 

 siderable size arising from the main nerve in the mandibular canal. It emerges 

 from the mandible through the mental foramen, and is distributed by many branches 

 to the chin and lower lip. It communicates, under cover of the facial muscles, with the 

 ramus marginalis mandibulse of the facial nerve (Fig. 657, p. 783). (3) The incisor 



