ANATOMY. 
other. The marrow occupies the tube left 
in the middle of the long bones, and also 
tills the cancelii of their extremities. 
The cellular substance, which contains 
the marrow, being condensed upon the in- 
side of the walls of the bone, and adhering 
to them, has been termed the periosteum in- 
ternum. 
We observe in the principal bones arte- 
ries, much larger than those which nourish 
the bone, penetrating these bodies obliquely, 
and spreading their branches upon the me- 
dullary cells. 
Various unsatisfactory opinions have been 
proposed concerning the use of the marrow. 
The utility of the bones being formed as 
they are, small and tubular in the middle, 
expanded and spongy at their extremities, 
has been already explained. If then spaces 
are necessarily left in their interior parts, 
those spaces must be filled with something ; 
for they cannot be left void, or the immense 
pressure of the atmosphere would crush 
their sides, and destroy the vacuum. There 
is no matter in the animal body more suit- 
able to fill their spaces than the marrow ; 
aftd it is to be regarded as a part of the adi- 
pons system of the animal. 
From the circumstances which have been 
detailed in the foregoing account, viz. the 
great and general vascularity of bones ; the 
quantity of soft substance existing in every 
part of them ; their growth and mutation of 
form in disease, &c. it is natural to con- 
clude, that there exist in the composition of 
every bony fibre, arteries for its formation, 
absorbents for its removal, cellular sub- 
stance for the connexion of its parts, and 
nerves to give animation to the whole. In 
this view of the subject, we see no essential 
difference of structure between bones and 
other parts of the body : nor do we expect 
any essential difference in the functions of 
their nutrient and other vessels. W e natu- 
rally conclude that bony fibres are formed 
and repaired, and that they undergo muta- 
tion and removal in the same manner, and 
from the same causes that soft parts do. 
CARTILAGE 
is a semipellucid substance, of a milk-white 
or pearly colour, entering into the compo- 
sition of several parts of the body. It holds 
a middle rank, in point of firmness, between 
bones or hard parts, and the softer consti- 
tuents of the human frame. It appears, on 
a superficial examination, to he homoge- 
neous in its .texture ; for, when cut, the sur- 
face is uniform, and contains no visible cells, 
cavities, nor pores ; but resembles the sec- 
tion of a piece of glue. It possesses a very 
high degree of elasticity ; which property 
distinguishes it from all other parts of the 
body. Hence it enters into the composition 
of parts, whose functions require the com- 
bination of firmness with pliancy and flexi- 
bility : the preservation of a certain exter- 
nal form, with the power of yielding to ex- 
ternal force or pressure. 
Cartilages are covered by a membrane, 
resembling, in texture and appearance, as 
well as in its office, the periosteum of bones : 
this is termed the perichondrium. They re- 
ceive arteries and veins from this mem- 
brane : these vessels, however, have never 
been demonstrated in the cartilaginous 
crusts of articular surfaces. Absorbent ves- 
sels cannot be actually shewn, but their ex- 
istence is abundantly proved by many phe- 
nomena. The conversion of cartilage into 
bone is alone sufficient for this purpose. 
The cartilaginous substance is gradually re- 
moved, as the formation of the bone ad- 
vances. In affections of the joints, their 
cartilaginous coverings are often both en- 
tirely destroyed, or partially removed ; 
which appearances can only be ascribed to 
the action of absorbent vessels. 
It does not seem to possess nerves, as it 
is entirely destitute of sensibility. 
The thinner cartilages of the body are re- 
solved by maceration into a kind of fibrous 
substance : e. g. those of the organs of sense. 
Those of the ribs are found by long mace- 
ration to consist of concentric oval lamina*. 
In some there are tendinous fibres inter- 
mixed; as in those of the vertebrae. 
Anatomists divide cartilages into two 
kinds : the temporary and the permanent. 
The former are confined to the earlier stages 
of existence ; the latter commonly retain 
their cartilaginous structure throughout 
every period of life. 
The temporary cartilages are those in 
which the bones of the body are formed. 
They are hence called by the Latin writers 
ossescentes. All the bones of the body, ex- 
cept the teeth, are formed in a nidus of 
cartilage. The form of the bone, with its 
various processes, is accurately represented 
in these cartilaginous primordia ; and it is 
tiie substance alone which changes. 
The permanent cartilages are of various 
kinds. We find them composing the exter- 
nal ear, external aperture of the nostrils, 
and eye-lids. The larynx is entirely com- 
posed of this substance j and the trachea, 
with its branches, is furhished with cartila- 
