THE MANDIBULAR NERVE 941 



(fig. 743). It then gives off the sublingual nerve, which runs forward to supply the sublingual 

 gland and the neighbouring mucous membrane (fig. 743). Its terminal (lingual) branches are 

 derived chiefly from the glosso-palatine nerve. They pierce the muscular substance of the 

 tongue and are distributed to the mucous membrane of its anterior two-thirds. They interlace 

 with similar branches of the other side and with branches of the glosso-pharyngeal nerve. 



The inferior alveolar (dental) nerve is the largest branch of the posterior 

 portion of the mandibular nerve. It commences on the medial side of the ex- 

 ternal pterygoid muscle and descends to the interval between the spheno-man- 

 dibular ligament and the ramus of the mandible, where it receives one or two 

 communicating branches from the lingual nerve. Opposite the middle of the 

 medial surface of the ramus it enters the mandibular (inferior dental) canal, ac- 

 companied by the inferior alveolar (dental) artery, which lies in front of the nerve, 

 and it runs downward and forward through the ramus and the body of the 

 mandible (fig. 736). At the mental foramen it divides into two parts, one of 

 which, the mental nerve, passes out through the mental foramen, the other, com- 

 monly called the incisive branch, continues forward in the canal, and supplies, 

 through the inferior dental plexus, the inferior canine and incisor teeth and the 

 corresponding regions of the gums. 



Branches. — The branches of the inferior alveolar (dental) nerve are branches 

 forming the inferior dental plexus, and the mental branch. A bundle of motor 

 fibres, the mylohyoid nerve, a branch of the masticator nerve, is given off just 

 before the inferior alevolar nerve enters the mandibular canal. 



The inferior dental plexus is formed by a series of branches which communicate with one 

 another within the bone, giving rise to a fine network. From this plexus two sets of branches 

 are given off: — the inferior dental branches, corresponding in number to the roots of the teeth, 

 enter the minute foramina of the apices of the roots and end in the pulp; the second set, the 

 inferior gingival branches, supply the gums. 



The mental nerve is a nerve of considerable size which emerges through the mental foramen 

 (fig. 736). It communicates, near its exit from the bone, with branches of the facial nerve, and 

 then divides into three branches. The smallest branch, turning downward, divides into several 

 twigs, the mental branches, which supply the integument of the chin. The other two, inferior 

 labial branches, pass upward, diverging as they ascend, and divide into a number of twigs. 

 The stoutest twigs ramify to the mucous membrane which lines the lower lip. Other twigs 

 are distributed to the integument and fascia of the lip and chin. 



The auriculo -temporal nerve usually arises from the posterior portion of the 

 mandibular nerve by two roots which embrace the middle meningeal artery and 

 unite behind it to form the trunk of the nerve. The trunk passes backward on 

 the medial aspect of the pterygoideus externus, and between the spheno-man- 

 dibular ligament and the temporo-mandibular articulation, lying in close relation 

 with the capsule of the joint. Behind the joint it enters the upper part of the 

 parotid gland, through which it turns upward and lateralward. It emerges from 

 the upper end of the gland, crosses the root of the zygoma close to the posterior 

 border of the superficial temporal artery, and divides into auricular and temporal 

 terminal branches at the level of the tragus of the pinna (fig. 736) . 



Communications. — (a) Each of the two roots of the nerve receives a communication from 

 the otic ganglion containing fibres derived from the glosso-pharyngeal nerve. These fibres 

 have passed from the glosso-pharyngeal through the tympanic plexus and the small superficial 

 petrosal nerve and through the otic ganglion. 



(6) Sensory filaments pass from the auriculo-temporal nerve to the temporo-facial branch 

 of the facial nerve. 



(c) Filaments of connection with the sympathetic plexus on the internal maxiUary artery. 



(d) A communication to the inferior alveolar (dental) nerve. 



Branches of the auriculo-temporal nerve. — (a) An articular branch to the temporo-man- 

 dibular joint, given off as the nerve lies on the medial side of the capsule. 



(6) Branches to the external auditory meatus. Two branches, as a rule, are given off in 

 the parotid gland. They enter the meatus by passing between the cartilage and the bone and 

 supply the upper part of the meatus, the membrana tympani by a fine branch, and occasionally 

 the lower branch gives twigs to the skin of the lobule of the pinna. 



(c) Parotid branches are distributed to the substance of the parotid gland. Sensory or 

 trigeminal fibres for the gland spring either directly from the nerve or from the communicating 

 branches previously given by it to the glosso-palatine nerve. The parotid branches also con- 

 tain fibres derived from the glosso-pharyngeal nerve which pass successively through its tym- 

 panic branch, the tympanic plexus, the small superficial petrosal nerve, the otic ganglion, and 

 the communicating twigs from the otic ganglion to the roots of the auriculo-temporal nerve. 

 The parotid branches are later again mentioned as concerned chiefly with the gangliated 

 cephalic plexus. 



(d) The anterior auricular branches, usually two in number, are distributed to the skin 

 of the tragus and the upper and outer part of the pinna. 



