758 THE NERVOUS SYSTEM 



I'rum l>et\veen the heads of the external pterygoid, it gives off a slender twig to the 

 temporal niusel(\ 



The POSTERIOR PORTION of the mandihiilar division of the fifth nerve divides 

 into three large branehes; two of these, the auriculo-teniporal and the lingual, are 

 exelusively sensory; the remaining branch, mandil)ular (inferior dental), contains 

 a strand of motor fibres — the mylo-hyoid nerve. 



(1) The auriculo-temporal nerve arises by two roots, whicli usually embrace 

 the middle meningeal artery, and ])asses backwards and outwards between the 

 internal lateral ligament of the temp()ro-mandil)ular articulation and the condyle of 

 the mandible, closely eml)racing the ca])sular ligaments of the joint. It then ascends 

 under cover of the parotid gland and traverses the glandular substance as it 

 crosses the root of the zygoma. It accompanies the temporal artery, being placed 

 under cover of and slightly behind that vessel, and terminates at the level of the 

 tragus of the ear by dividing into auricular and temporal branches. As it passes 

 through the parotid gland it communicates with the temporo-facial division of the 

 facial nerve by two stout twigs, which may surround the temporal artery. The 

 auriculo-temporal nerve receives conmiunicating twigs from the otic ganglion, and 

 gives off the articular branch, the nerves to the meatus, and the parotid branches. 

 It terminates in the anterior auricular and superficial temporal branches. 



(a) The communicating twigs from the otic ganglion join the nerve close 

 to its commencement in the form of several fine filaments. 



These filaments have been shown by physiological experiments to be derived from the glosso- 

 pharyngeal nerve through the lesser superficial petrosal. They run for a short distance in the 

 trunk of the auriculo-temporal, and leave it under the name of parotid branches. They are the 

 secreto-motor fibres of the jiarotid gland. 



(6) The articular branch is supplied to the temporo-mandibular articulati(Mi 

 as the auriculo-temporal nerve is passing between the capsular ligament and the 

 parotid gland. 



(c) The nerves to the meatus, two in number, pass between the bony and 

 cartilaginous parts of the external auditory meatus and supply the skin lining the 

 meatus. The upper of the two nerves furnishes a filament to the upper and anterior 

 l>art of the membrana tympani. The lower nerve gives twigs to the lobule of the 

 ear. Occasionally only the upper nerve is present, the lower being replaced by a 

 twig from the great auricular. (Henle. ) 



(d ) The parotid branches are a variable number of fine twigs which arise either 

 directly from tlie auriculo-temporal nerve or from the loops of communication 

 between it and the facial. As al )ove mentioned, they supply the glandular sul)stance. 



(e) The anterior auricular branches, two in numl)er, are sup|)lied to the 

 upper part of the pinna, and are chiefly distributed to the integument which coveis 

 the anterior asjiect of the tragus and helix. 



(/) The superficial temporal branches divide at acute angles and ramify 

 over the integument which covers the temporal fascia. The largest twig accom- 

 })anies the posterior branch of the temporal artery. The anterior twigs communi- 

 cate with the tenijxiral branches of the facial nerve. 



(2) The mandibular (inferior dental) nerve is the largest branch of the 

 mandil)ular division. It passes downwards under cover of the external pterygoid 

 muscle to reach the interval between the ramus of the lower jaw and the spheno- 

 mandibular ligament. In this situation it is placed on the outer side of and some- 

 what l)ehind the lingual nerve, and is connected to the latter by a transverse com- 

 municating branch. It then enters the mandibular canal accompanied by the 

 mandibular artery, and lies at first behind and then below that vessel as it follows 

 the course of the canal. Opposite the mental foramen it terminates by dividing 

 into an incisive and a mental branch. The branches of the inferior dental nerve 

 are the mylo-hyoid, the alveolar, tlie incisive, and the mental. 



(a) The mylo-hyoid is given off from the mandibular nerve immediately 

 before the latter enters the dental canal. It runs downwards and forwards in the 

 mylo-hyoid groove of the mandible between the bone and the internal pterygoid 

 muscle. In this course it is accompanied by the mylo-hyoid artery. It then runs 

 forwards on the inferior surface of the mylo-hyoid muscle, under cover of the sub- 



