ANATOMY, 
thin sheets of compacted and close cellular 
texture. This is proved by long maceration 
in water. The fluid gradually penetrates the 
interstices, and resolves the membrane into 
a loose and floculent substance. They are 
found in every variety of density and softness. 
A grand use of membranes is to line what 
anatomists call the, circumscribed cavities of 
the body. These are hollow spaces, con- 
taining the different viscera, and in every 
instance completely and accurately filled by 
such viscera ; so that the term cavity, when 
used by anatomists, does not, as in common 
language, denote a void or empty space. 
Membranes have a smooth internal po- 
lished surface, turned towards the contained 
viscera. , This is constantly moistened by a 
lubricating fluid exhaled by the minute ar- 
teries of the part, and bestows on the sur- 
face of the membrane the greatest softness 
and smoothness. Hence the motions of the 
viscera are performed with perfect facility, 
and they are prevented from adhering to 
each other, or to the sides of the containing 
cavity. The extent of such cavities is 
bounded and defined by the lining mem- 
branes, and hence arises the epithet circu/n- 
sa-ibed. To increase the facility of motion, 
the surface of the contained viscera is co- 
vered by productions of the same mem- 
brane, and always therefore possesses the 
same smoothness and polish with the sides 
of the cavity. In the carcase of an ani- 
mal just slaughtered, the lubricating secre- 
tion flies off in the form of a fine vapour, 
when the cavity of the belly or chest is laid 
epen. It is nothing more than an increase 
of this natural secretion, combined perhaps 
with a deficient absorption, that gives rise 
to dropsies of the different cavities. 
The opposite or external surface of the 
membrane is rough and cellular ; and ad- 
heres to the various parts, which form the 
sides of the cavity. 
Another use of membranes is to form 
blood-vessels, or tubes, for conveying the 
nutritious fluid to all parts of the body. The 
bore or hollow of the tube is perfectly smooth 
and polished, so that the blood experiences 
no obstruction in its course ; and the exter- 
nal surface is rough, to connect it with the 
surrounding parts. In a similar manner are 
formed the stomach and intestines, which 
r eceive the food ; the urinary bladder, 
which holds the urine, &c. 
It must be obvious, that for all the pur- 
poses which we have enumerated, whether 
for lining circumscribed cavities, for con- 
veying the blood, for receiving the food, or 
holding any other liquors, it is essentially 
necessary that membranes should be imper- 
meable to fluids in the living state. 
OSTEOLOGY. 
The bones are the most solid parts of the 
body. They are composed of a vascular 
substance, not differing materially in struc- 
ture from that of the rest off the body, ex- 
cept that there is deposited in its interstices 
an earthy matter, which gives to the whole 
mass rigidity, strength, and a permanent fi- 
gure. The nutrient vessels of arteries, mem- 
branes, and ligaments, occasionally deposit 
lime, and cause the ossification of those 
parts. 
The account of the original formation of 
the bones in thefoetus, is technically termed 
osteogeny. The parts of the young foetus, 
which are afterwards to become bones, are 
at first cartilaginous ; and their substance is 
rendered white and firm in proportion to 
the quantity of lime deposited in it. The 
quantity at the time of birth is only suffi- 
cient to give firmness to the whole mass, 
not to prevent its flexibility. 
, The extremities of all the long bones con- 
sist of large portions of cartilage, and these, 
by degrees become bony. The formation 
of bone begins in the centre of the cartilage, 
and gradually extends from thence to the 
remote parts, so that the separate piece of' 
bone, formed at the extremity, remains till 
near the time of puberty, conjoined to the 
body of the bone by a crust of cartilage. In 
this state it is technically termed an epiphy- 
sis. The body, or middle part of the bone, 
is called the diaphysis. The projecting 
parts, or processes of bones, are also in 
many instances originally epiphyses. The 
time by which these epiphyses are consoli- 
dated by a bony union with the diaphysis, 
varies in different bones, but it is not pro- 
longed in any much beyond the age of pu- 
berty. 
We perceive an evident advantage in the 
bones of the foetus being formed as they are. 
Their flexibility admits of the form of the 
limbs becoming adapted to tiie varying fi- 
gure of the pelvis, through which they must 
pass ; and their elasticity, which is power- 
ful, restores them afterwards to their natural 
shape. 
The animal substance contained in bones 
is demonstrated by immersion in weak acids, 
which dissolve the earth, and leave a kind 
of cartilage similar to that in which the bone 
was originally formed. Long boiling in a 
close vessel removes the gelatinous sub- 
