| AA Oe 
plates or laminx 
other ; an afcending one from the lining of the vein to the 
their pofition as compared to the heart ; but in the above 
defeription we fuppofe the veffel to be going firaight to the 
heart. "The extremities of the loofe edge, where they are 
connected to the fides of the vein, are prolonged in a narrow 
form, fo as to reprefent the two horns of a crefcent, thefe 
are called the cornua, and vary in length. hefe folds are 
extremely thin, but itrong, and poffels a fomewhat fhinin 
appearance; according to Haller they often prefent fora- 
i da reticulated appearance, as if they had given 
way to the force of the blood. 
every valve we diftinguith the fixed edge by which the 
ning of the vein, which i i 
hich the convex apex is 
turned from the heart, and the fides are continued along the 
tube of the vein towards that organ: hence, 
is intercepted, 
2 and reprefenting, when 
diftended with wax, a parabolic cone, longer or fhorter in 
different inftances. 
in the larger trunks thefe folds are generally arranged in 
pairs, as at the 
ves are frequently found in the {maller veffels, as in thofe 
of the hand and foot: thefe are at the fame time generally 
longer. Haller has feen fuch in the {permatic and vena 
ay os, and fays that they are fometimes found in the extre- 
mities, and fhut the whole canal of the vein: when elevated. 
Branches fometimes join venous trunks without any valves at 
their Openings, and then there is a fimple round opening with 
» a8 at the origin of an arteri — P sciaso? 
ere are valves juft at the orifice, formed by the 
membrane of a branch, : : 
_ The fize of the valves is proportioned to that of the veffel 
an which e found; but they are not always fuffi- 
ciently to clofe it completely. This circumitance, 
hich has attracted the attention of moft anatomiits, who 
refer it to the original formation of the parts, is explained 
by Bichat by the varying ftate of the calibre of the tube. 
* 
‘When the vein is confiderably dilated the valves, which do 
not yield in the fame proportion, are rendered fmaller with 
or coronary veins, excepting the ogi one at the mouth of 
1 
vt 
veins, where, how- 
ever, they are not numerous. ey are found in fuch 
ranches of the hypogattric veins as do not go to the uterus 
ble numbers exift in the crural and popliteal : 
they are found at the opening of the faphena Ls i of the 
faphena minor, and in their ramifications. 
In deferibing the fituations, where valves are found in the 
branches of the fuperior cava, we come firft to the vena azy- 
gos, about which much controverfy has arifen on this point. 
Fallopius and Euftachius deny their exiftence in this vein, 
and Haller afferts, as an excufe for their error, that fluids, in- 
jeCted into the fuperior cava, will always fill the trunk and © 
branches of this veffel. arious anatomilts, a i 
Bartholin, Senac, and de 
A 
large pair of valves is placed at the inferior end of the inter- 
nal jugular vein ; which, however, allow the 
jection. In the 1 
of the body, 
is the « 
with a pair of valves, which prevent the blood from 
where they are very numerous: 
appearance of thefe veins in injected prepa 
Bae four pairs to the trunk of the bafilic 
bow and its termination, and the fame number tot 
vein in the fame diftance. 
then, in general, that thefe folds are chiefly found 
perpendicular fituation, as in the limbs, 
and the vena azygos: 
the limbs, and in the cutaneous veffels, 
rations, — 
between the el- 
he brachial 
: 
and are h: 
the whole vary 
confiderably. The moft convenient mode of exhibiting them 
is by placing a vein, flit up, in wi ter.” ge 
The ¢ the valves, in preventing the blood from re- 
turning through the veins, in a courfe contrary to that of its 
casa Saevel, is fo obvious, that it need hardly be infitted 
on. ‘Thefe thin folds lie clofe to the fide of the veffel, apd 
offer no obitacle to the blood’s ceurfe ; but when that fluid 
is repelled in the vein, # lifts the hoofe edge, enters the finns, 
and 
