618 NERVOUS SYSTEM. 



in the chapters on digestion, except as regards the action of the filaments sent to the 

 muscles of the velum palati. In deglutition, the muscles of mastication are indirectly 

 involved. This act cannot he well performed unless the mouth be closed hy these muscles. 

 When the food is brought in contact with the velum palati, muscles are brought into 

 action which render this membrane tense, so that the opening is adapted to the size of 

 the alimentary bolus. These muscles are animated by the motor root of the fifth. This 

 nerve, then, is not only the nerve of mastication, animating all of the muscles concerned 

 in this act, except two of the most unimportant depressors of the lower jaw (the genio- 

 hyoid and the platysma myoides), but it is concerned indirectly in deglutition. 



Facial Nerve, or Nerve of Expression (the Portio Dura of the Seventh 



Nerve). 



The facial, the portio dura of the seventh according to the arrangement of Willis, is 

 one of the most interesting of the cranial nerves. Its anatomical relations are quite intri- 

 cate, and its communications with other nerves, very numerous. As far as can be deter- 

 mined by experiments upon living animals, this nerve is exclusively motor at its origin ; 

 but in its course it presents anastomoses with the sympathetic, with branches of the fifth, 

 and with the cervical nerves, undoubtedly receiving sensory filaments. While the chief 

 physiological interest attached to this nerve depends upon its action upon muscles, it is 

 important to study its origin, distribution, and communications. 



Physiological Anatomy of the Facial Nerve. The portio dura of the seventh has its 

 apparent origin from the lateral portion of the medulla oblongata, in the groove between 

 the olivary and the restiform body, just below the border of the pons Varolii, its trunk 

 being internal to the trunk of the portio mollis, or auditory nerve. It is separated from 

 the auditory by the two filaments constituting what is known as the intermediary nerve 

 of Wrisberg, or the portio inter duram et mollem. As this little nerve joins the facial, 

 it must be included in its root. 



There are certain pathological considerations which render the deep, or real origin of 

 the facial a question of the greatest interest and importance. In hemiplegia due to injury 

 of the substance of the encephalon, particularly from haemorrhage, there is almost always 

 more or less paralysis of the superficial muscles of the face. It has been observed that, 

 in certain cases, the facial paralysis exists upon the same side as the hemiplegia (the side 

 opposite to the cerebral lesion), while in others, the palsy of the face is upon the same side 

 as the lesion, the general hemiplegia being, as usual, upon the opposite side. To explain 

 these phenomena theoretically, we must assume that, in some cases, the brain-lesion is to 

 be located at a. point where it involves the filaments of origin of the facial (following 

 them from without inward) before they decussate, which would produce facial paralysis 

 upon the same side as the lesion and none upon the side affected with general hemiplegia; 

 while, in other cases, the injury to the brain involves the roots of the facial after they 

 have decussated, when the paralysis of the face would be upon the same side as the paraly- 

 sis of the rest of the body. It "would be interesting to see how far these pathological 

 fact:;, with their theoretical explanation, correspond with anatomical researches into the 

 real origin of the nerves. 



Many anatomists have endeavored to trace the fibres of the facial from their point of 

 emergence from the encephalon to their true origin, but with results not entirely satis- 

 factory. At the present day, it is pretty generally agreed that the fibres pass inward, 

 with one or two deviations from a straight course, to the floor of the fourth ventricle, 

 where they spread out and become fan-shaped. In the floor of the fourth ventricle, cer- 

 tain of the fibres have been thought to terminate in the cells of the gray substance, and 

 others have been traced to the median line, where they decussate ; the course of most of 

 the fibres, however, has never been satisfactorily established. 



