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ANATOMY: 99 
OF MUCILAGE SACS, AND JOINTS. 
Those surfaces of bones which form the moveable joints, are in- 
vested, besides the cap and other ligaments, by a thin delicate mem: 
brane. ‘I'he mucilaginous membrane forms a complete sac or bag, 
which covers the particular surface of one bone, and is reflected from 
it to the corresponding surfaces of the other ; adhering firmly to each 
of the joint surfaces, and extending loosely from the margin of one 
surface to that of the other: $ — gue ie 
At is thin and very flexible, but ainosg It secretes or effuses from 
its surface a liquor called mucilage ; which is particularly calculated 
to lubricate the parts that move upon each other. This fluid is very 
nearly transparent: it has the consistence of a thin syrup, and is 
very tenacious or ropy. . 
There are, in many of the joints, masses of fat, which appear to 
project into the cavity, but are exterior to the mucilage membrane, 
They are generally situated so as to be pressed gently, but not bruised 
by the motions of the bones. : Ld ai 
_ ‘The mucus membrane, like other parts of the joints, is insensible 
in a sound state; but extremely painful when inflamed: 
There is another species of mucus bags, which are found between 
the tendons and bones, near the joints, and in other places also.— 
They are formed of a thin dense mem brane, and are attached to the 
ite 
surrounding parts by cellular substance ; they contain a mucus fluid 3_ = 
and sometimes there are masses of fat, which; although exterior to 
them, appear to project into their cavities. 
. They often communicate with the cavities of the joints; and being» 
always situated upon parts that move upon each other, their use, un 
doubtedly is, to lessen friction. Sb dyer: ‘ + settee 
These mucus bagsare very numerous, and some of them are very 
interesting, on account of their connexion with important joints; _ 
but as a particular description of them would be tedious, and of little. 
benefit, it is omitted: 
t=. = ——s 
” 
DOCTRINE OF THE VESSELS. 
Vessels are long membranous canals, which carry blood, lymph, or 
chyle. They are divided into arteries, veins; and absorbents. Ex- _ 
cept the scarf skin and thé nails, every part of the body has vessels; 
as injections demonstrate: = ae 
