324 MR. BELL ON THE NERVES OF THE FACE. 



We may for a moment interrupt our particular inquiry, to notice that all 

 muscular nei*ves, and consequently the muscular divisions of the fifth nerve, 

 form a plexus. The plexus, formed by the motor and ganglionic divisions of the 

 fifth nerve before they diverge to the muscles of the lower jaw, corresponds with 

 the plexus formed on the nerves sent to other classes of muscles. Even that 

 branch of the third division of the fifth nerve which comes out before the ear, 

 joins the portio dura in a plexus*; and this is the reason of that sensibility 

 evinced in the facial nerve in making experiments upon it. 



The form of the fifth nerve, and its resemblance to the spinal nerves, had 

 struck some of the best continental anatomists. But as they had made no 

 distinctions in the functions of the roots of the spinal nei'ves, so neither did 

 they imagine any difference in the roots of the fifth nerve, and therefore no 

 consequence resulted from having observed this resemblance. This part of 

 the anatomy, together with the whole minute relations of the nerves, was a 

 dead letter, and led to no inference. 



But now resuming the course I have hitherto followed, the anatomy of the 

 fifth nerve points to curious results. We see that the motor division of this 

 nerve goes first to the muscles which close the jaw and give it the lateral or 

 grinding motions. Secondly, we see that it is distributed to the muscles of 

 the cheek, which place the morsel under the operation of the teeth; and thirdly, 

 we find it going to the muscles which open the jaws. 



We proceed to the second method of proof, by experiment. Does the fifth 

 nerve move the jaw ? is it indeed the manducatory nei*ve as suggested by 

 the anatomy ? Let the following experiments determine the fact. 



EXPERIMEINT I. 



The root of the fifth nerve being exposed in an ass and irritated, the jaws 

 closed with a snap. 



Experiment II. 



The fifth pair being divided in an ass, the jaw fell relaxed and powerless. 



If we consider the action of mastication, we shall see what the consequence 

 would be, were there no accordance between the motions of the lower jaw and 



• See the adjoined plate. 



