504 NERVOUS SYSTEM 



distributed to the temporal muscle. The buccal branch sends filaments 

 to the external pterygoid and the temporal muscles, and a small branch 

 is distributed to the internal pterygoid muscle. From the posterior 

 branch, which is chiefly sensory but contains some motor filaments, 

 branches are sent to the mylo-hyoid muscle and to the anterior belly 

 of the digastric. In addition the motor branch of the fifth sends fila- 

 ments to the tensor muscles of the velum palati. 



Experiments have shown that the buccinator muscle receives no 

 motor filaments from the fifth but is supplied entirely by the facial. 

 The buccal branch of the fifth sends motor filaments to the external 

 pterygoid and the temporal, its final branches of distribution being 

 sensory and going to integument and mucous membrane.. 



In treating of the physiology of digestion, a table has been given 

 of the muscles of mastication with a description of their action. It will 

 be seen by reference to this table that the following muscles depress the 

 lower jaw : the anterior belly of the digastric, the mylo-hyoid, the genio- 

 hyoid and the platysma myoides. Of these the digastric and the mylo- 

 hyoid are animated by the motor root of the fifth ; the genio-hyoid is 

 supplied by filaments from the sublingual ; and the platysma myoides, 

 by branches from the facial and from the cervical plexus. All the 

 muscles that elevate the lower jaw and move it laterally and antero- 

 posteriorly, namely, the temporal, masseter, and the internal and 

 external pyterygoids, the muscles most actively concerned in mas- 

 tication, are animated by the motor root of the fifth. 



Properties and Uses of the Nerve of Mastication. The anatomical 

 distribution of the small root of the fifth nerve points at once to its uses. 

 Charles Bell called it the nerve of mastication, in 1821, although he did 

 not relate any experiments in regard to its action. Anatomical and 

 physiological writers since that time have adopted this view. It would 

 be difficult if not impossible to stimulate the root in the cranial cavity in 

 a living animal; but its faradization in animals just killed determines 

 movements of the lower jaw. Experiments have demonstrated the 

 physiological properties of the small root, which is without doubt a 

 nerve of motion only. 



There is little left to say in regard to the uses of the motor root of the 

 fifth nerve, in addition to the description of the action of the muscles of 

 mastication, contained 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 

 can not be well performed unless the mouth is closed by these muscles. 

 When the food comes in contact with the velum palati, muscles are 

 brought into action which render this membrane tense, so that the 



