FACIAL NEEVE. 781 



branch is the terminal part of the inferior alveolar nerve remaining after the origin 

 of the mental branch. It supplies the canine tooth and the incisor teeth. 



Ganglion Oticum. The otic ganglion is situated deep to the mandibular 

 nerve just below the foramen ovale. Like the other ganglia described above, it 

 possesses three roots : (1) A motor root, derived from the nerve to the internal 

 pterygoid muscle ; (2) a sensory root, formed by the lesser superficial petrosal nerve 

 from the tympanic plexus (through which communications are effected with the 

 tympanic branch of the glossopharyngeal nerve, and a branch from the genicular 

 ganglion of the facial nerve); (3) a sympathetic root, from the plexus on the 

 middle meningeal artery (Fig. 656). 



Five branches arise from the ganglion three communicating and two motor 

 branches. The three communicating nerves are fine branches which join respectively 

 the nerve of the pterygoid canal, the roots of the auriculo-temporal nerve, and the 

 chorda tympani nerve. The two motor nerves supply the tensor tympani and 

 tensor veli palatini muscles. 



Summary. The trigeminal, the largest and most complex of the cerebral nerves, is (1) the 

 chief sensory nerve for the face, the anterior half of the scalp, the orbit and eyeball, the nose and 

 nasal cavity, the lips, teeth, mouth, and anterior two-thirds of the tongue ; (2) the motor fibres 

 of the nerve supply the muscles of mastication, the mylo-hyoid and anterior belly of the digastric, 

 possibly the levator veli palatini and uvular muscle (through the spheno-palatine ganglion), and 

 the tensor tympani and tensor veli palatini muscles (through the otic ganglion) ; (3) through the 

 ganglia placed on the three divisions of the nerve, not only are important organs, areas, and 

 muscles innervated, but communications are also effected with the sympathetic system, with the 

 oculo-motor nerve (ciliary ganglion), facial nerve (spheno-palatine and otic ganglia), and glosso- 

 pharyngeal nerve (otic ganglion). 



In its distribution to the skin of the face the branches of the fifth nerve present two striking 

 peculiarities : (1) While the branches to the skin reach the surface at many points and in 

 diverse ways, the three main divisions are severally, by their branches, responsible for the supply 

 of three clearly demarcated cutaneous areas (Fig. 648, p. 772). (2) By numerous communications 

 with the facial nerve, sensory fibres are given to the muscles of expression supplied by the* 

 facial nerve. 



NERVUS ABDUCENS. 



The sixth or abducens nerve issues from the brain at the inferior border of 

 the pons, just above the pyramid of the medulla oblongata (for the deep origin, see 

 p. 600). It is directed forwards, it pierces the dura mater in the posterior 

 fossa of the base of the skull alongside the dorsum sellse, and enters the cavernous 

 sinus (Fig. 647, p. 771). In the sinus it is placed close to the lateral side of the 

 internal carotid artery. After it leaves the sinus it passes through the superior 

 orbital fissure below the oculo-motor and naso-ciliary nerves and between the two 

 heads of the lateral rectus muscle (Fig. 652, p. 776). In the cavity of the orbit it 

 supplies the lateral rectus muscle on its deep (ocular) surface. 



Communications. In the wall of the cavernous sinus the sixth nerve receives two 

 communicating filaments : (1) From the carotid plexus of the sympathetic, and (2) from 

 the ophthalmic division of the trigeminal nerve. 



NERVUS FACIALIS. 



The seventh or facial nerve emerges from the brain at the inferior border of 

 the pons, below the trigeminal nerve and medial to the acoustic nerve (for the deep 

 origin, see p. 598). Between it and the acoustic nerve is the minute nervus inter - 

 medius (Fig. 656, p. 782). The facial nerve passes through the internal acoustic 

 meatus, and through the canalis facialis in the petrous portion of the temporal bone, 

 emerges at the base of the skull by the stylo-mastoid foramen, and passes forwards 

 through the parotid gland to supply the muscles of the face. In the internal 

 acoustic meatus the nerve is placed upon the acoustic nerve, the nervus intermedius 

 intervening. In the canalis facialis the nerve first passes forwards and laterally 

 to the hiatus of the canal, then backwards on the medial side of the tympanum, 

 and finally downwards behind the tympanum, in the medial wall of the tympanic 

 antrum. In the parotid gland it crosses the external carotid artery and the posterior 

 facial vein superficially. On the face its branches radiate from the anterior border 

 of the parotid gland and enter the deep surface of the facial muscles. 



