166 Mr. Bell on the nervous circle which connects 
nerve of motion. It arises in two roots, one of these is the 
muscular nerve, the other the sensible nerve ; on this last 
division the Gasserian ganglion is formed. But we can trace 
the motor nerve clear of the ganglion and onward in its 
course to the muscles of the jaws, and so it enters the tem- 
poral masseter pterygoid and buccinator muscles. 
If all that is necessary to the action of a muscle be a nerve 
to excite to contraction, these branches should have been 
unaccompanied ; but on the contrary, I found that before 
these motor nerves entered the several muscles, they were 
joined by branches of the nerves which came through the 
Gasserian ganglion, and which were sensitive nerves. 
I found the same result on tracing motor nerves into the 
orbit, and that the sensitive division of the fifth pair of nerves 
was transmitted to the muscles of the eye, although these 
muscles were supplied by the third, fourth, and sixth nerves. 
A circumstance observed on minute dissection remained 
unexplained, — when motor nerves are proceeding to several 
muscles they form a plexus ; that is, an interlacement and 
exchange of fibres takes place. 
The muscles have no connection with each other, they are 
combined by the nerves ; but these nerves, instead of passing 
betwixt the muscles, interchange their fibres before their dis- 
tribution to them, and by this means combine the muscles 
into classes. The question therefore may thus be stated : 
why are nerves, whose office it is to convey sensation, pro- 
fusely given to muscles in addition to those motor nerves 
which are given to excite their motions ? and why do both 
classes of muscular nerves form plexus ? 
To solve this question, we must determine whether muscles 
