278 HEAD AND NECK 



(O.T. inferior dental) is the largest branch of the mandibular 

 nerve. Emerging from under cover of the external pterygoid, 

 at the lower border of the muscle, it passes downwards upon 

 the spheno-mandibular ligament and enters the mandibular 

 foramen. The inferior alveolar artery runs downwards 

 posterior to it, whilst the lingual nerve is anterior to it 

 and upon a somewhat deeper plane. The inferior alveolar 

 is a sensory nerve, but a few fibres from the motor root 

 are prolonged downwards within its sheath as far as the 

 mandibular foramen. At this point they come off as the 

 slender fnylo-hyoid nerve. 



The mylo-hyoid nerve, accompanied by the artery of the 

 same name, pierces the spheno-mandibular ligament and 

 proceeds downwards and anteriorly in a groove upon the 

 inner surface of the mandible to the digastric triangle. A 

 narrow prolongation of the spheno - mandibular ligament 

 bridges over the groove and holds the nerve and vessel in 

 position. In the digastric triangle the mylo-hyoid nerve has 

 been dissected already (p. 230). It breaks up into numerous 

 branches for the supply of two muscles, viz., (i) the mylo- 

 hyoid, and (2) the anterior belly of the digastric. 



Nervus Lingualis. The lingual nerve is entirely sensory. 

 In the first part of its course, like the other branches of the 

 mandibular nerve, it lies medial to the external pterygoid 

 muscle. As it descends it appears at the lower border of 

 the muscle. Then it proceeds downwards and anteriorly, 

 between the internal pterygoid muscle and the mandible, and 

 enters the submaxillary region, where it will afterwards be 

 traced to the tongue. It lies anterior to and on a slightly 

 deeper plane than the inferior alveolar nerve. It gives off 

 no branches in the infratemporal region, but, whilst still 

 under cover of the external pterygoid, it is joined at an acute 

 angle by the chorda tympani branch of the facial nerve. Not 

 infrequently, also, a communicating twig passes between it 

 arid the inferior alveolar nerve. 



Chorda Tympani. This is a slender nerve which arises 

 from the facial in the canalis nervi facialis (O.T. aqueduct of 

 Fallopius). It gains the infratemporal region by traversing 

 the tympanic cavity and appearing through the medial part 

 of the petro-tym panic fissure (O.T. Glaserian), whence it runs 

 downwards and anteriorly, medial to the spheno-mandibular 

 ligament. It is joined by a slender filament from the otic 



