THE ENCEPHALIC OR CRANIAL NERVES 641 



THE SEVENTH NERVE. THE FACIAL 



The seventh cranial nerve, the facial, consists of peripherally coursing 

 nerve-fibers, which serve to bring the nerve-cells from which they arise 

 into relation with most of the superficial muscles of the head and face. 



The muscles supplied by this nerve, as stated by the general anatomists, 

 are as follows: The occipito-frontalis, corrugator supercilli, orbicularis 

 palpebrarum, levator labii superioris alaeque nasi, zygomatici, the pyramidalis 

 nasi, compressor nasi, depressor alae nasi, levator anguli oris, buccinator, 

 orbicularis oris, depressor anguli oris, depressor labii inferioris, levator 

 menti, posterior belly of the digastric, stylohyoid, and platysma myoides. 

 These muscles by their individual and cooperative contraction express ideas 

 and feelings and are therefore termed muscles of expression. 



Origin. The nerve-fibers or axons composing the seventh nerve arise 

 for the most part from a nucleus of large multipolar nerve-cells situated 

 about five millimeters beneath the upper half of the floor of the fourth ven 

 tricle toward the middle line. 



From this nucleus, which is about four millimeters long, axons emerge 

 which at first pass inward and backward as far as the ependyma of the ven- 

 tricle; they then turn on themselves, forming an arch that encloses the nu- 

 cleus of the sixth nerve; they then course downward and outward, emerging 

 from the pons at its lower border between the olivary and restiform bodies. 

 As the axons approach the floor of the ventricle collateral branches are 

 given off which, crossing the median line, arborize around the nerve-cells 

 of the opposite facial nucleus. 



Clinic observations and histologic investigations, however, render it 

 probable that the fibers distributed to the occipito-frontalis, the corrugator 

 supercilii, and the upper half of the orbicularis palpebrarum, are derived 

 from the oculo-motor nucleus, and, descending the posterior longitudinal 

 bundle, enter the trunk of the facial as it turns to pass forward through the 

 pons. It is also probable, for similar reasons, that the fibers distributed to 

 the orbicularis oris are derived from the hypoglossal nucleus. 



Cortical Connections. The nucleus of the facial nerve is in histologic 

 and physiologic connection with the facial region of the general motor area 

 of the cerebral cortex. From the cells of this region axons descend through 

 the pyramidal tract, the internal capsule, and the crus cerebri, heyond which 

 they cross to the opposite side and arborize around the cells of the nucleus 

 already described. 



Distribution. From its superficial origin the trunk of the nerve passes 

 into the internal auditory meatus beside the auditory nerve. After passing 

 forward and outward for a short distance through the bone above and be- 

 tween the cochlea and vestibule, the nerve makes a sharp bend, forming the 

 genu facialis, turns backward and enters the aqueduct of Fallopius, the gen- 

 eral course of which it follows as far as the stylo-mastoid foramen. After 

 emerging from this foramen the nerve passes downward and forward as far 

 as the parotid gland, within which it terminates by dividing into two main 

 branches, the temporo-facial and the cervico-facial, the ultimate branches 

 of which are distributed as previously stated to the superficial muscles of the 

 head and face. 



Properties. Electric stimulation of the trunk of the nerve after its emer- 

 gence from the stylo-mastoid foramen produces convulsive movements in all 

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