122 
MR. YOUATT’s VETERINARY LECTURES. 
ing more closely, we discover that it is the larger or superior part 
that forms the ganglion, while the inferior portion can be traced 
beyond the ganglion, until it afterwards unites with its fellow 
to form the perfect nerve. 
The Double Function of the Fifth Pair .—These things had 
been pretty well known to some of the best anatomists ; but it re¬ 
mained for Sir Charles Bell to draw from them the legitimate and 
important conclusion that this is a nerve of double function—of 
sensation and of voluntary motion. He laid bare the root of the 
fifth pair in an ass, immediately after the animal was killed, and 
on irritating the nerve, the muscles of the jaw acted, and the jaw 
was closed. He divided the root of the nerve in a living animal, 
and the jaw T fell. There seemed to be no contradicting this. It 
had been admitted on all hands, that the fifth was a nerve of 
sensibility ; it seemed now evident that it was also a nerve of 
motion. Sir Charles, however, pursued his experiment one step 
further; he selected the superior maxillary branch of the fifth 
pair, w 7 hose ramifications extend to the muzzle, and he divided it 
on both sides: the power of elevating and projecting the lip, as 
in gathering the food, was lost; and in order to open the lips, the 
animal pressed his mouth against the ground, and at length 
licked up the oats with his tongue. 
Mr. Mayo's Experiments. —Mr. Mayo instituted experiments 
of a similar nature; and although he differed from Sir Charles 
Bell in some conclusions which he drew respecting the respira¬ 
tory nerves, yet he arrived at a similar result as to the loss of 
power in the lips ; for when he divided the second and third 
branches, the lips no longer remained in perfect apposition, and 
the animal ceased to use them in taking up his food. He, how¬ 
ever, ingeniously accounts for this by the loss of sensibility in the 
part; and he tells us very truly, that when the sense of feeling is 
taken away from a part, the voluntary muscles cannot be effici¬ 
ently excited. 
Some Muscles are supplied by the Fifth Pair alone. —There 
are, however, some anatomical facts which incontestably prove 
that the fifth is a motor nerve ; for there are certain muscles of 
great power, and particularly the masseter, the temporal, and the 
two pterigoids, which are principally or entirely supplied by the 
fifth pair, and therefore must derive from those nerves their power 
of motion as well as of feeling. 
The probable Roots of Motor and Sensitive Power. —Then, as 
the inferior root arises from the inferior surface of the prolonga¬ 
tion of the spinal chord, and (what we shall better understand 
when we have examined the spinal chord) it passes by, and does 
not help to form the ganglion, and its fibres are minute, it is pro- 
