540 THE CRANIAL NERVES. 



to Dean, 1 stellate, oval, or fusiform nerve cells, among which the nerve 

 fibres penetrate. The nucleus constitutes, at this situation, the gray 

 matter of the " fasciculus teres." The fibres of the abducens and facial 

 nerves are given off from its internal and external borders respectively ; 

 those of the abducens passing directly downward through the tuber 

 annulare, near the median plane, those of the facial first passing out- 

 ward and then bending downward, to reach their point of emergence at 

 the posterior edge of the lateral portion of the pons Varolii. 



According to Dean, Meynert, and Henle, a considerable portion of the 

 root fibres of the facial nerve communicate, either directly or through 

 the nucleus, across the median line, with the opposite side of the brain. 



After emerging from the posterior edge of the pons Varolii, the facial 

 nerve, in company with the auditory, passes into and through the in- 

 ternal auditory meatus. It then enters, by itself, the aqueduct of Fal- 

 lopius, and, following the course of this canal through the petrous 

 portion of the temporal bone, comes out at the stylomastoid foramen 

 and turns forward upon the side of the face. It spreads out between 

 the lobules of the parotid gland into a number of branches, which by 

 their mutual interlacement form the well-known " parotid plexus," or 

 " pes anserinus," of this nerve. Its branches then diverge upward, for- 

 ward, and downward, to be distributed to the superficial muscles of the 

 facial region. It also supplies, by branches given off immediately after 

 its emergence from the stylomastoid foramen, the muscles of the exter- 

 nal ear, as well as the stylohyoid and the posterior belly of the digastric ; 

 and by a twig which descends below the jaw to the submaxillary region, 

 it supplies filaments to the upper part of the platysma myoides muscle, 

 and communicates with an ascending branch of the superficial cervical 

 nerve from the cervical plexus. 



Physiological Properties of the Facial Nerve. The facial is shown, 

 by the result of abundant corresponding investigations, to be, at its 

 origin and in its main physiological characters, an exclusively motor 

 nerve. Not only is the tactile sensibility of the facial region imme- 

 diate^ destroyed by the section of the fifth pair within the skull, 

 though the facial itself remain uninjured, but, according to the ex- 

 periments of Magendie and Bernard, the trunk of this nerve, when irri- 

 tated at its source in the living animal, after opening the cranial cavity, 

 shows no sign of sensibility, although that of the sensitive cranial 

 nerves is at the same time perfectly manifest. On the other hand, 

 Chaveau has found that in the recently killed animal, galvanization of 

 the intracranial portion of the facial nerve causes at once contraction 

 of the muscles of the face and of the external ear. This nerve is accord- 

 ingly, at its source, insensible and excitable. 



Furthermore, the most decisive results are obtained from division of 

 the facial nerve at various parts of its course. This may be done, in 



1 Gray Substance of the Medulla Oblongata and Trapezium. Washington, 

 1864, pp. 58, 61. 



