THE ACOUSTIC NERVE 803 



in the parotid gland behind the superficial temporal artery, and terminates in 

 anterior auricular and temporal branches. The small anterior auricular branches 

 form with the frontal and lacrimal branches of the trigeminus the anterior auricular 

 plexus. They innervate the anterior auricular and parotido-auricularis muscles. 

 The temporal branch runs forward and inward over the temporal muscle to the 

 medial canthus of the eye, forms a plexus with the terminal branches of the ophthal- 

 mic nerve, and is distributed to the orbicularis oculi, corrugator supercilii, and 

 levator nasolabialis. 



10. The cervical branch (R. colli) (Fig. 560) is small; it arises from the ventral 

 border of the facial opposite to the preceding nerve. It passes obliquely through the 

 parotid gland, emerging under cover of the parotido-auricularis, passes downward 

 and backward on or near the jugular vein, and anastomoses with the cutaneous 

 branches of the cervical nerves. It gives branches to the parotido-auricularis and 

 the cervical cutaneous muscle. In its course along the neck the nerve is reinforced 

 by twigs from the cutaneous branches of the second to the sixth cervical nerves. 



11. Small branches are detached to the guttural pouch and the parotid gland. 

 The latter (Rami parotidei) concur with branches of the superficial temporal nerve 

 in forming the parotid plexus. 



The facial nerve usually terminates after a short course on the surface of the 

 masseter by dividing into two buccal branches (Fig. 560). 



1. The dorsal buccal nerve (N. buccalis dorsalis) passes forward on the upper 

 part of the masseter, dips under the zygomaticus, and reaches the ventral border of 

 the dilatator naris lateralis. It continues under cover of the last-named muscle 

 and the levator nasolabialis in company with the superior labial artery and ramifies 

 in the muscles of the upper lip and nostril. It gives collateral branches to the 

 buccinator and anastomoses with the infraorbital and ventral buccal nerve. 



2. The ventral buccal nerve (N. buccalis ventralis) crosses the masseter 

 obliquely and continues forward along the depressor labii inferioris. It is connected 

 by variable anastomotic branches with the dorsal nerve. It gives collateral 

 branches to the cutaneus, buccinator, and depressor labii inferioris, and ramifies 

 in the muscles of the lower lip. 



The buccal nerves are subject to much variation in regard to their course, anastomoses, 

 and relations to the sensory components derived from the superficial temporal nerve. Their 

 distribution is constant. The point at which the branch of the superficial temporal nerve joins 

 the facial is variable. 



THE ACOUSTIC NERVE 



The acoustic nerve (N. acusticus) is connected with the lateral aspect of the 

 medulla just behind and lateral to the facial (Fig. 629). It has two roots, vestib- 

 ular and cochlear (Radix vestibularis, cochlearis). 



The acoustic nerve consists of two distinct parts which might well be regarded as separate 

 nerves. The cochlear part mediates the sense of hearing, while the vestibular part is not auditory 

 in function, but is concerned in the sense of the position of the body and the mechanism of 

 equilibration. 



The nerve passes outward to the internal acoustic meatus, which it enters 

 behind the facial nerve. In the meatus it divides into two nerves, of which the 

 upper is the vestibular and the lower is the cochlear nerve. 



1. The vestibular nerve (N. vestibuli) is distributed to the utriculus, the saccu- 

 lus, and to the ampullae of the semicircular ducts of the internal ear. In the 

 internal acoustic meatus the nerve is connected by filaments with the geniculate 

 ganglion of the facial nerve. At the bottom of the meatus it bears the vestibular 

 ganglion (G. vestibulare), from the cells of which the fibers of the nerve arise. 



2. The cochlear nerve (N. cochleae) detaches a filament to the sacculus, passes 



