324 
MR, BELL ON THE NERVES OF THE FACE. 
We may for a moment interrupt our particular inquiry, to notice that all 
muscular nerves, 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 nerves, 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 nerve as suggested by 
the anatomy? Let the following experiments determine the fact. 
Experiment 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. 
