182 HEAD AND NECK 



At that point they separate off as the slender mylo-hyoid 

 nerve (Figs. 63, 68). 



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

 same name, pierces the spheno-mandibular ligament and 

 proceeds downwards and forwards, in a groove upon the 

 medial 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. 129). 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 (Fig. 68). 



Nervns 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 

 and the inferior alveolar nerve. 



Chorda Tympani. The chorda tympani 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 forwards, medial to the 

 spheno-mandibular ligament. It is joined by a slender 

 filament from the otic ganglion, and it unites with the lingual 

 nerve a short distance below the upper end of the latter. 



Dissection. The student should now endeavour, by means 

 of a Key's saw, a chisel, and the bone forceps, to remove the 

 outer table of the mandible, and thus open up the mandibular 

 canal. 



Structures within the Mandibular Canal. The mandibular 

 canal is traversed by the inferior alveolar vessels and nerve, 

 which give off twigs to the roots of the molar and praemolar 



