ANATOMY. 
lygoid branch of the superior maxillary. In 
the, upper part of the neck this nerve has a 
very large ganglion lying on the vertebrae, 
called the superior cervical ganglion. This 
ganglion receives branches of communica- 
tion from the five, upper pairs of cervical 
nerves, and sends off a branch to the heart. 
The trunk descends along the neck, and 
forms an inferior cervical ganglion, which 
lias communicating filaments from the 
neighbouring spinal nerves, and sends seve- 
ral branches to the heart, forming the car- 
diac plexus. The sympathetic nerve then 
passes through the chest, over the heads of 
the ribs, receiving branches from each dor- 
sal nerve, and forming a dorsal ganglion be- 
tween every two vertebrae. In its course 
it sends off the splanchnic nerves, which go 
through the diaphragm, and form a vast and 
most intimate plexus about the root of the 
caeliac artery, called the caeliac plexus, from 
v. hi eli the liver, pancreas, spleen, large 
and small intestines, and kidneys derive 
their nerves. Ail these organs receive se- 
veral filaments united so as to form plex- 
uses, and surrounding their arterial trunks. 
The trunk of the great sympathetic en- 
ters the abdomen, and goes over the lumbar 
vertebrae, receiving branches of communi- 
cation, and forming lumbar ganglia ; it is 
then continued along the front of the sa- 
crum, where the sacral nerves supply com- 
municating filaments, and where five sa- 
cral ganglia are formed. 
ORGANS OF SENSE. 
Organ of vision .- — The globe of the eye is 
contained in a bony socket, formed by the 
bones of the cranium and of the face. It is 
furnished with muscles which can move it in 
every direction, and surrounded by a very 
soft and delicate kind of fat, which yields 
to it in all its motions. It is composed of 
certain membranes, called its tunics or 
coats, and of other parts termed humours. 
Its figure is very nearly spherical ; but 
the transparent portion in front is the sec- 
tion of a smaller sphere than the globe. The 
optic nerve, to which the eyg-ball is attach- 
ed posteriorly, enters considerably on the 
inside of the axis of the eye. 
The coats of the eye are disposed con- 
centrically ; and the exterior, which is very 
dense, firm, and tough, is called the sclero- 
tica. This does not cover the whole globe, 
but leaves a circular opening in front, filled 
lsy the transparent cornea, which, although 
pellucid, is a very firm and strong mem- 
brane. Hence the sclerotica and cornea 
together form a very complete exterior case; 
which defends and supports the more deli- 
cate parts within. The necessity of having 
the front of the globe transparent, for the 
purpose of admitting the rays of light, is 
obvious. 
Under the sclerotica a soft and vascular 
membrane surrounds the eye-ball, and is 
called the choroid coat. It is connected to 
the sclerotica by a loose adhesion, which 
can be destroyed by blowing air between 
the membranes ; but in front this adhesion 
is stronger, and forms a white circle, named 
orbiculns or ligamentum ciliare. The co- 
lour of the choroid coat is a deep brown, 
<ip pro aching to a black, and this colour is 
derived from a substance called pigmentum 
nigrum, which separates from the choroid by 
maceration, and dissolves in water so as to 
render it turbid. 
The inner surface of the choroid coat, 
which is universally coloured by pigmentum 
nigrum in the human subject, is sometimes 
called tunica ruyschiana ; as Rnysch endea- 
voured to prove that it formed a distinct 
membrane from the external part. It is 
this inner surface that possesses the brilliant 
colours observable in animals, whence the 
appellation of tapetum. This surface lies 
in contact with the retina, but does not ad- 
here to that membrane. On the front of 
the eye however, and beyond the anterior 
margin of the retina, the choroid is closely 
attached by means of numerous and very 
delicate folds, called the ciliary processes, 
to tiie surface of the vitreus humour, round 
the margin of the crystalline lens. 
The iris is a membrane continued trans- 
versely across the eye-ball, behind the cor- 
nea, and appearing as a continuation of the 
. choroid from the orbiculus ciliaris. The 
round opening in the front of this mem- 
brane is called the pupil : it allows the pas- 
sage of the rays of light into the interior of 
the eye. This aperture varies in its dimen- 
sions, according to the quantity of light to 
which the organ is exposed : a strong light 
causes the pupil to become contracted, in 
order to exclude a portion of the rays of 
light, which offend the organ. The aper- 
ture is dilated in a weak light, to let in as 
many rays as possible. Some anatomists 
have thought proper to employ themselves 
in debating at length whether these motions 
arise from a really muscular structure or no 5 
but we believe that they have not yet set- 
tled the point completely. 
The name of iris was applied to this part, 
from the diversity of colours observable in 
