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ANATOMY. 
Thus the veins, in many particulars, refemble the arte¬ 
ries. 'I here are fix ; of which two anlwer to the aorta, 
and tire remaining four to the pulmonary artery. Some 
count a feventh trunk, by taking in the venae hepaticse. 
Their balis is in the auricles of the heart, and their apices 
in the extremities of each branch through all parts of the 
body, excepting one inftance in the liver; or we may re- 
verfe this order, and fay the veins terminate in the heart. 
They often run parallel with, and accompany, the arteries. 
The fabric of the veins is tender, every where fmooth, 
difficultly feparable into diftinft coats or membranes, like 
the arteries ; and the cellular texture furrounding them is 
very ealily diftended. The veins both above and below 
the heart are furrounded, except in one place, with muf- 
cular fibres ; every where, however, their lubftance is lax, 
like the cellular texture which joins the arteries to the 
adjacent parts; the veins are, neverthelefs, every where 
fufficiently firm, and do not eafily burft with inflated air; 
being in molt infiances ftronger than the arteries them- 
lelves. But they burft much more eafily in living than in 
dead animals, as appears from morbid infiances in the arm, 
face, leg, thigh, &c. They do not preferve their cylin¬ 
drical form after having been cut, but collapfe together, 
fo as to make their capacity appear like a flit; except they 
are fuftained, and hindered from thus collapling, by forn.e 
ftrong cellular fubftance placed round them, as we fee in 
the liver and w omb. They are only flightly irritable, un- 
lefs the ftlmulus be of the chemical or more acrid clafs ; 
for, in that cafe, they contract themfelves with a convul- 
five force greater than that of the arteries. They have no 
pulfation, unlefs the venous channel is fomewhat obftruct- 
ed; or when, in dying people, the blood is thrown back 
again from the right auricle into the dclcending and af- 
cending cava, or w hen falling back from the brain. 
The veins are much larger than their correfponding ar¬ 
teries, having the fquare of their diameter often double or 
triple, or almoft quadruple ; as maybe feen near the emul- 
gents and veflels of the kidneys. In general, however, the 
diameter of the veins is to that of the arteries as nine to 
four ; yet the capacity of the capillary veins but little ex¬ 
ceeds that of the arteries which accompany them, 'they 
differ likewife from the arteries in their divifion, having 
more numerous trunks and branches; for to one artery in 
the limbs, we ufually meet with two veins : and there are 
many veins, as the external jugular, vena portarum, azy¬ 
gos, cephalic, bafilic, and faphena, w ith which there are no 
coi refponding‘urt.eries. The larger veins are alio branched 
in a more net-like difpofition, by forming more frequent 
anaftomofes with one another than the arteries do. Many 
of the veins run near the fur face of the body, efpecially in 
the limbs, neck, and head ; they run a long way covered 
with little more than the bare fkin, which is a circum- 
ffance we very rarely obferve in arteries ; and, for the 
fame reafon, they often feparate from the arteries; fol¬ 
lowing the furiace of the parts next the (kin, without their 
correfponding artery, which defeends to a conliderable 
depth, attended in its courfe by fome fmall venous branch. 
In the fmaller branches of the veflels, where they make 
net-like difpofilions in the membranes and the internal fa¬ 
bric of the viicera, the veins and arteries commonly run 
contiguous one to the other; but here the veins have gene¬ 
rally a lefs Terpentine or in lie died courfe than the arteries. 
In the larger fanguineous veins, valves arc found in great 
The inriermoft, membrane of the vein, being 
, rifles into the cavity of the veffel like a curtain, 
lb-etching itfelf farther along the vein every way, fo as to 
form what may be called a kind of crefcent; but the bafis, 
which is the part that luftains the weight of the blood, is 
ftrongeft, and grows out of the vein in thefhape of a cir¬ 
cular fegment. The valve intercepts a fpace, of which 
the outer lide is the vein it fell', and the inner the valve ; 
which, by its convexity, projefts within the bore of the 
vein, fo that the parabolic fpace or hollow mouth of the 
v alve is always turned towards, the heart. They are found 
in all the fubcutaneous veins or the, limbs, in thofe of the 
plenty. 
doubled 
neck, face, tongue, and penis: at the origin of the larger 
branches, there are two, three, four, and fometimes five, 
of them together, while in the fmaller branches they are 
only (ingle. Thefe valves are wanting in the veins of the 
deep-feated vifeera; namely, the brain, lungs, heart, and 
liver, and through the whole lyllem of the vena portarum. 
They are alfo wanting in the kidneys and womb, (except 
one or two valves.in the fpermatic vein ;) and, laftly, in 
thofe fmall blood-veins which are lefs than the twelfth 
part of an inch in diameter. Sometimes, though rarely., 
they are found in the branches of the vena azygos, and at 
the mouths of the hepatic and renal veins; where Dr.Haller 
has fometimes obferved a fort cf wrinkles in the place of 
valves. In the fmaller venous branches there are a let of 
long (harp-pointed or parabolical valves, of a more extended 
figure as the vein is fmaller, which feem to refill the return 
of the blood more powerfully titan the larger-valves. 
The veins have theirorigin, as we laid before, from the 
terminations of the arteries. They fometimes arife by a 
continuation from the inferted branches, or frojn a reflec¬ 
tion of recurved trunks of the finalleit arteries. Others, 
again, are continued from veins lefs than thofe which 
carry blood; and alfo, in Dr. Haller’s opinion, from the 
absorbing veins ; but, as abforption by the red veins is now 
denied, that opinion muft be rejected. Yet, that there are 
veins of a fmaller clafs, but refembling thofe which con¬ 
vey blood, appears from the fame experiments which de- 
mon(Irate the pellucid'arteries; thus there are fmall veins 
in the iris, and in the adnata tunica of the eye; nor is it to 
be doubted, that, in a healthy fubjeft, fmall pellucid veins 
may be found in the vitreous body of the eye itfelf. Such 
have been fometimes feen by Wrifberg and others, after 
a fine injedtion or inflammation in the capfules of the lens 
and vitreous humour. 
Hie Anatomical Plate VII. reprefents a juft delineation 
of the Heart and Blood-Vessels; and of which the 
following is an explanation. 
FRONT VIEW. 
A, The heart. B, The aorta afeendens. C, A trunk 
from which the right fubclavian and right carotid arteries 
are fent oft'. ( Thofe on the left fide come oft' feparately.) 
The fubclavian artery palfes over to the arm behind the 
fubclavian vein. The carotid artery runs up to the head, 
partly covered by the internal jugular vein. D, The facial 
artery, which fends oft' the coronary arteries of the lips; 
E, The deep temporal artery. F, The defeending aorta. 
G, The right common iliac artery, which divides into the 
external and internal iliacs. H, The femoral artery, which 
is a continuation of the external iliac artery. I, The an¬ 
terior tibial artery, fending branches to the fore-part of 
the leg and upper-part of the foot. 
i, The frontal vein running down to form 2, The facial 
vein. 3, Deep temporal vein. 4, Occipital vein. 5, The 
external jugular vein. 6, The internal jugular vein, ly¬ 
ing on the outer and fore-part of the common carotid ar¬ 
tery. 7, An arch on the palm of the hand, which runs 
partly to 8, The radial vein, and partly to 9, The ulnar 
vein. (The two laft veins run clofe by the (ides of their 
correfponding arteries.) 10, The cephalic vein. 11, The 
bafilic vein, cut: on the left fide it is entire. 12, Branches 
running up to form 13, The humeral vein. 14, The ex¬ 
ternal thoracic veins running along with their arteries. 
(In many parts, the veffels are fo fmall, that one trunk 
muft repfefent both artery and vein.) 15, The axillary- 
vein. 16, The fubclavian vein, receiving the jugular and 
other veins from the head and neck. 17, The vena cava 
fuperior. 18, Veins from the upper-part of the foot form¬ 
ing 19, The anterior tibial vein, which lies clofe by the 
fide of the correfponding artery. 20, The venae profundae 
femoris. 21, The upper part of the vena faphena. 22, The 
femoral vein. 23, The common iliac veins, formed of 
the external and internal iliacs. 24, Vena cava inferior. 
25, The renal veins covering the arteries. 2 6, The dia¬ 
phragmatic veins. 
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