5 25 A N A T 
of the human machine. All bones are covered by a mem¬ 
brane, named on that account pa iofieum .; and except where 
mufcles, cartilages, or ligaments, are inferted into the pe- 
riofteum, its external furface is conneXed to the furround- 
ing parts by thin cellular membranes, which can eafily be 
ltretched conliderably, but Ihorten themfelves wlienever 
the ftretching force is removed. When thefe membranes 
are cut off or broken, they coilapfe into fuch a fmali fpace, 
that the furface of the perioiteum 1'eems fmooth and 
.equal. 
The internal periojleum is an extremely fine membrane 
lining the inlide of the bone. It hath procelfies entering 
into the tranfverfe pores of the bones, where probably 
they are continued to form the intermediate canals for the 
marrow diftributed through the fubfiance of the bones ; 
.and along with them velfels are fent, as from the external 
perioiteum, into the bone. Thefe proceffes being of a 
very delicate texture, the adhelion of this membrane to 
the bone is fo fmali, that it feparates commonly more ea- 
lily from the bone than from the marrow which it con¬ 
tains : wherefore one might call it the common membrane 
-of the marrow, rather than by the name it now has. But 
whether the one or the other delignation ought to be given 
it, is not worthy a difpute. 
The marrow is the oily part of the blood, feparated by 
fmali arteries, and depofited in thefe cells. Its colour 
and confiflence may therefore vary according to the Hate 
of the velfels, and their diftribution on the membranes of 
the cells. The marrow is bloody in children, oily and 
balmy in middle age, and thin and watery in old people. 
By experiments made on the marrow when bones of living 
animals are opened or cut through, and from the racking 
jpain with which fuppurations within bones are frequently 
attended, we have Sufficient proof that the membranes 
here are fenfible, and confequently have nerves diftributed 
to them. Hippocrates might therefore fay juftly, that a 
wound penetrating into the cavity of a bone may produce 
a delirium. 
Cartilages are folid, fmooth, white, elafiic, fubflances, 
between the hardnefs of bones and ligaments, and cover¬ 
ed with a membrane, named perichondrium ; which is of the 
fame ftruXure and ufe to them, as the periofteum is to the 
bones. While cartilages are in a natural ftate, it is to be 
remarked, ill, That they have no cavity in their middle 
for marrow. 2dly, That their outer furface is fofteft, 
which renders them more flexible. 3d 1 y', That they do 
not appear to change their texture near fo much by acids, 
as bones do. And, laftly, That as the fpecific gravity of 
cartilages is near a third lefs than that of bones; fo the 
cohefion of their feveral plates is not fo ffrongasin bones; 
whence cartilages, laid bare in wounds or ulcers, are not 
only more liable to corrupt, but exfoliate much fooner 
than bones do. 
Ligaments are white flexible -bodies, thicker and firmer 
than membranes, and not fo hard or firm as cartilages, 
without any remarkable cavity in their fubfiance, diffi¬ 
cultly flrctched, and with little elafticity ; lerving to con¬ 
ned: one part to another, or to prevent the parts to which 
they are fixed from being removed out of that fituation 
which is ufeful and fafe. Authors generally fay that liga¬ 
ments are infenlible ; and confequently it may be inferred, 
that they have no nerves bellowed on them. But the vio¬ 
lent racking pain felt on the leaft motion of a joint labour¬ 
ing under a rhenmatifm, the feat of which difeafe feems 
often to be in the ligaments, and the infufferable torture 
occafioned by incifions of ligaments, and by a collection 
of acrid matter in a joint, or by tophi in the-gout, per- 
fuade us that they are abundantly itipplied with nerves. 
-Part of the capfular ligaments is compofed of the periof- 
ieum, continued from one bone to another, and their in¬ 
ternal layer is continued on the parts of the bone or carti¬ 
lage which the ligament includes. Befides thefe common 
capfular ligaments of the joints, there are particular ones 
in feveral places, either for the firmer connection of the 
articulated bones, or for refiruining and confining the mo- 
O M Y. 
tion to fome one fide; fuch are the n o/s and lateral liga« 
ments of the knee, the round one of the thigh, &c. 
Synovia is the liquor which principally ferves to moiften 
the ligaments and cartilages of the articulations, and is 
fupplied by glands, which are commonly lituated in the 
joint, after fuch a manner as to be gently prefied, but not 
deftroyed by its motion. By this means, when there is 
the greateft neceflity for this liquor, that is, when the molt 
frequent motions are performed, the greateft quantity of 
it muft be feparated. Thefe glands are foft and pappy, 
but not friable: in fome of the large joints they are of 
the conglomerate kind, or a great number of fmali glan¬ 
dules are wrapt up in one common membrane. Their ex¬ 
cretory duCts are long, and hang loofe, like fo many 
fringes, within the articulation; which, by its motion and 
prelfure, prevents obftruXions in the body of the gland 
or its excretories, and promotes the return of this liquor, 
when fit to be taken up by the abforbent velfels, which 
muft be in the joints, as well as in the other cavities of 
the body; and, at the fame time, the prelfure on the ex¬ 
cretory duXs hinders a fuperfiuous unnecelfary fecretion, 
while the fimbriated difpofition of thefe excretories does 
not allow any of the fecreted liquor to be puffied back 
again by thefe canals towards the glands. Very often thefe 
fountains of flimy liquor appear only as a net-work of 
velfels. Frequently they are almoft concealed by cellular 
membranes containing the fat; and fometimes fmali fim- 
ple mpeous folliculi may be feen. The different joints 
have thefe organs indifferent numbers and fizes : the con¬ 
glomerate ones do not vary much, efpecially as to fitua¬ 
tion, in the limilar joints of different bodies; but the. 
others are more uncertain. 
The name of fibre is given to fmali filaments, which ap¬ 
pear to be the mod fimple parts of the body, and which, 
by their different difpofition and connexions, compofeall 
the other parts. The fibres differ in Jubilance, being ei¬ 
ther membranous, flelhy, tendinous, or bony; in direXion, 
being either ftraight, oblique, longitudinal, tranfverfe, cir¬ 
cular, or fpiral; and in fize, being either large, fmali, long, 
or fliort. 
By membrane, we underftand a pliable texture of fibres 
1 interwoven or difpofed together in the fame plane, They 
differ in thicknefs, according to the fmallnefs of their fi¬ 
bres and number of their planes. Thefe particular planes 
are termed lamince, and are diftinguiffied into external, in¬ 
ternal, middle, &c. The difference of membranes in ge¬ 
neral depends on that of the fibres, of which they are 
compofed. Small portions of membranes, efpecially when 
they are very thin, are called pellicula:', and fome membra¬ 
nous laminae are united together by the intervention of a 
particular fubfiance, compofed of this fort of pellicles, 
and called the cellular or fipongyfiubfiance. 
By vcjficls are meant tubes, duXs, or canals, more or lefs 
flexible, comppfed of different membranes, the ftrata of 
which are generally termed tunica or coats. Some of them 
are divided into branches, and thefe again into rami and 
ramifications, which gradually diminilh, but fiill remain 
hollow. The general deiign of the velfels is to contain 
fluids; from the diverfity of which they are diftinguiffied 
into blood-veffels, vafa laXea, lymphatica, &c. The laft 
and fmallefi: extremities of all forts of vefiels are gene¬ 
rally termed capillaries. The blood-vejfcls are of two kinds; 
one of which receives the blood from the heart, and dif • 
tributes it to all the parts of the body, and are named 
arteries-, the other brings the blood back again from all 
parts to the heart, and are called veins ; and l’ome of thefe 
have the name of finufies. The arteries are thicker than 
the veins, and may be diftinguiffied by this mark in diffeX- 
ed dead bodies; and in living bodies they are known by a 
certain beating called the pvlfe. The trunks of the veins 
lie nearer the furface of the body than the arteries, and 
are furnifhed with valves, that is, with fmali membranous 
facculi, fixed at different diftances to the Tides of their 
cavities. The openings of thefe valves are broad, and 
turned toward the hearty but thea; bottoms are turned the 
y ' contrary 
