THE ENCEPHALIC OR CRANIAL NERVES 627 



? 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 ttie 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, beyond 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 

 the muscles to which its branches are distributed. The same results follow 

 stimulation of the intra-cranial portion of the nerve in an animal recently 

 killed. 



Irritative pathologic lesions e.g., tumors, aneurysms, etc. situated 

 along the course of the nerve or at its nuclear origin, or in the cortical or 

 sub-cortical regions, frequently give rise to spasmodic movements of the 

 facial muscles on one side, which may be tonic or clonic in character. 



Division of the facial nerve after its emergence from the stylo-mastoid 

 foramen is followed by a complete relaxation or paralysis of the superficial 

 facial muscles of the corresponding side. The same result follows compres- 

 sion of the nerve-trunk in any part of its intra-cranial course. 



The phenomena presented by an individual suffering from division or 

 compression of the facial nerve, and which collectively constitute facial paraly- 

 sis, are as follows: A relaxed and immobile condition of the side of the 



