ANATOMY. 
eeed in a straight uninterrupted course, but 
join frequently with each other. 
A nerve divided in the living subject re- 
tracts : the medulla is expressed from its 
extremities, by the contraction of its mem- 
branes, in the form of globules. If the 
animal be killed at some distance of time 
from the operation of dividing a nerve, the 
divided extremities are rather swoln, and 
are connected by a newly-formed matter. 
Anatomists have disputed greatly, whe- 
ther or not this be a real nerve. As 
this question can hardly be decided by 
merely anatomical testimony, it appears 
most philosophical to inquire, whether the 
new matter will perform the functions of a 
nerve ; and this has been completely proved 
by the experiments of Dr. Haighton, in the 
first part of the Philosophical Transactions, 
for the year 1795. 
In some parts of the nervous system, little 
tubercles, or knots, called ganglia, are found 
in the course of the nerve, and are usually 
formed by the concurrence of several 
branches. These bodies are of various 
figures, but generally flattened. They par- 
take more of the red colour than the trunks 
of the nerves on which they are formed, as 
they possess more numerous blood-vessels. 
They contain nervous fibres, surrounded by 
a firm vascular substance. 
By the term origin of a nerve, we under- 
stand its connection with the brain or spinal 
inarrow. This end is called its sensorial ex- 
tremity, being considered as the point to 
which it conveys the impressions made on 
it by external objects, and from which it 
receives the commands of the will to be 
transmitted to the organs which it supplies. 
There is considerable difference in form, 
structure, and consistence, between the in- 
dividual nerves. 
The nerves are arranged in pairs, as they 
are exactly similar on both sides of the 
body. Hence any pair of nerves consists 
of the right and left nerve. 
They are sometimes divided into those of 
the brain, and those of the medulla spinalis ; 
or into the nerves of the organs of sense, 
the nerves of motion, and the mixed 
nerves ; or, according to the nature of the 
parts, which they supply, into voluntary 
and involuntary nerves. 
The quantity of nerves distributed to the 
different structures in the body varies great- 
ly. The organs of sense receive the most 
copious supply — viz. the eye, nose, laby- 
rinth of the ear, ends of the fingers, glans 
penis et clitoridis, and the rest of the skin. 
Muscles have also a large share of nerves ; 
the blood-vessels are much more sparingly 
furnished. The nerves of the viscera are 
very small in proportion to the size of the 
organs. Bones, cartilages, tendons, liga- 
ments, membranes, marrow, fat, have no 
discernible nerves. 
Nerves ramify through the body some- 
thing like arteries: thus, a nervous trunk 
sends off branches ; these, again divided, 
form ramifications : and in their further 
progress form twigs, filaments, &c. and this 
division goes on until the nerve, from its 
smallness can be no longer traced. Yet we 
can manifestly discern the nerves in some 
instances, as in the organs of sense, termi- 
nating in a pulpy expansion. 
Like the arteries, nerves communicate 
with each other ; and it is conjectured that 
these communications, like those of the 
blood-vessels, are designed to obviate the 
effects of the injury of compression of any 
particular nervous trunk. In some parts 
these communications are very numerous, 
so as to constitute a minute net-work of 
nervous filaments, called a plexus. 
Description of the particular nerves . — 
There are in the whole body thirty-nine 
pairs of nerves ; of which nine arise from 
the brain, and thirty from the spinal mar- 
row. There is another pair, called the 
great sympathetic, which can hardly be 
ascribed to either of these classes. 
Nerves of the brain. 
1st pair. Olfactory nerves ; arise front the 
corpora striata, and go through the cribri- 
form lamella of the ethmoid bone to the pi- 
tuitary membrane of the nose. 
2nd pair. Optic nerves ; arise from the 
thalami nervorum opticorum, and proceed 
to the eye-ball, where they are expanded 
to form the retin*. 
3rd pair. Nervi motores oculorum ; arise 
from the crura cerebri, and are distributed 
to some of the muscles of the eye-ball. 
4th pair. Nervi trochleares ; come from 
the valve of the brain, and supply the 
trochlearis muscle of the eye. 
5th pair. Nervi trigemini ; arise from the 
side of the medulla oblongata. This nerve 
divides ■ into three branches, of which the 
first, or ophthalmic, goes into the orbit, and 
after giving a few branches there, passes 
out on the forehead. The second, or supe- 
rior maxillary, supplies the parts about the 
upper jaw ; a remarkable branch of it is 
the infra-orbital which comes through the 
large hole under the orbit to the face. The 
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