THE FACIAL NERVE 943 



branches derived from the anterior portion are the deep temporal nerves, the 

 masseteric nerve, and the nerve to the external pterygoid. One branch, the 

 mylo-hyoid nerve, is carried in the posterior portion of the mandibular and is given 

 off from its inferior alveolar branch. 



The nerve to the internal pterygoid passes under cover of a dense layer of fascia derived 

 from an expansion of the Ugamentum pterygo-spinosum, and enters the deep surface of the 

 muscle. Near its commencement this nerve furnishes a visceral motor root to the otic ganglion, 

 and small twigs to the tensor tympani and tensor palati. 



The deep temporal nerves, usually two in number, posterior and anterior, pass between the 

 bone and the upper border of the external pterygoid muscle, and turn upward around the infra- 

 temporal crest of the sphenoid bone to end in the deep surface of the temporalis (fig. 736). 

 The posterior of the two often arises in common with the masseteric nerve. The anterior is 

 frequently associated with the buccinator (long buccal) nerve till the latter has passed between 

 the two heads of the pterygoideus externus. There is frequently a third branch, the medius, 

 which passes lateralward above the pterygoideus externus, and turns upward close to the bone 

 to enter the deep surface of that muscle. A small strand of masticator fibres accompanies the 

 buccinator nerve to enter and end in the anterior part of the temporal muscle. 



The masseteric nerve, which frequently arises in common with the posterior deep temporal 

 nerve, passes between the bone and the pterygoideus externus, and accompanies the masseteric 

 artery through the notch of the mandible to be distributed to the masseter (fig. 736). It is 

 easily traced through the deeper fibres nearly to the anterior border of the masseter. As 

 it emerges above the pterygoideus externus it gives off a twig to the temporo-mandibular 

 articulation. 



The nerve to the external pterygoid, after a course of about 3 mm. (an eighth of an inch), 

 divides into twigs which enter the deep surface of the two heads of the muscle. It is usually 

 adherent at its origin to the buccinator nerve. 



The mylo-hyoid branch, carried in the posterior portion of the mandibular nerve, is given 

 off immediately before the inferior alveolar (dental) nerve enters the mandibular (inferior dental) 

 canal. It pierces the lower and back part of the spheno-mandibular Ugament and runs down- 

 ward and forward in the mylo-hyoid groove between the mandible on the lateral side, and the 

 internal pterygoid muscle and the lateral surface of the submaxillary gland on the medial side. 

 In the anterior part of the digastric triangle it is continued forward between the anterior part 

 of the submaxillary gland and the mylo-hyoideus, and it breaks up into branches which supply 

 the mylo-hyoideus and the anterior belly of the digastric (fig. 736). 



THE FACIAL NERVE 



The facial or seventh nerve is purely motor. It is accompanied a short 

 distance by a bundle usually called its sensory root or the intermediate nerve. 

 This latter, however, on the basis of its origin, distribution, and mixed instead of 

 sensory character, is described separately below as the glosso-palatine nerve. 

 It is smaller than the facial, is fused to the trunk of the facial and the ganglion 

 giving rise to its sensory fibres is situated upon the external genu of the facial 

 (figs. 738 and 741). 



The fibres of the facial nerve (fig. 738) spring from a nucleus of cells situated 

 laterally in the reticular formation at the level of the lower pons, dorsal to the supe- 

 rior olive, and between the root fibres of the abducens nerve and the laterally placed 

 spinal tract of the trigeminus. From this nucleus the fibres of the nerve pass 

 medially and dorsal ward to the floor of the fourth ventricle and, just under the 

 floor, they turn anteriorly, passing dorsal to the nucleus of the abducens (fig. 653, 

 p. 827). At the anterior end of this nucleus they turn sharply ventralward and 

 lateralward, and at this point it is claimed that fibres descending in the near-by 

 medial longitudinal fasciculus from the nucleus of the oculo-motor nerve of the 

 same side become intermingled with the fibres of the facial nerve and pass 

 outward with them. This, however, is uncertain. Continuing ventralward 

 through the reticular formation the fibres of the facial emerge from the brain-stem 

 at the inferior border of the pons, lateral to the superficial attachment of the 

 abducens. At the point of its emergence, the facial nerve pierces the pia mater, 

 from which it receives a sheath, and then proceeds forward and lateralward 

 in the posterior fossa of the cranium to the internal auditory meatus, which it 

 enters in company with the glosso-palatine nerve and with the cochlear and 

 vestibular nerves. As it lies in the meatus it is situated above and in front of 

 the latter nerves, from which it is separated by the glosso-palatine, and it is 

 surrounded, together with these three nerves, by sheaths of both the arachnoid 

 and the dura mater and by prolongations of the subarachnoid and sub-dural 

 spaces. While it is still in the meatus it blends with the glosso-palatine and thus 

 the combined trunk is formed. At the outer end of the meatus the trunk pierces 



