ANATOMY. 
goes to the mufculi abdominis reCti. Having quitted the 
abdomen, it is called arteria cruralis, which runs down 
upon the thigh, and is diftri bitted by many branches and 
ramifications to all the lower extremity. 
The arteries themfelves have arteries which are more 
particularly fpread through their external cellular coat, 
which fpring on all Tides from the next adjacent fmall ar¬ 
terial trunks : they are numerous, and like net-work ; they 
are very minute, but plainly appear, even in the foetus, 
without injection. Nerves alfo defcend, for a long way 
together, through the furface of the artery, and at laft 
vanilh in the cellular fubftance of the velTel ; of which we 
have a fpecimen in the external and internal carotids, and 
in the arch of the aorta ; and Dr. Waller has lhewn them 
in feveral arteries in the thorax and abdomen. Do not the 
arteries feem to derive from thefe nerves a mufcular and 
convullive force, very different from that of their fimple 
elafticity ? Does not this force (hew itfelf plainly enough 
in fevers, faintings, pal Ties accompanied with atrophy, and 
paflions of the mind ? Haller conliders the artery as being 
in a manner infenfible and unirritable; and if it is con- 
ftricted by the application of poifons, he fays it has every 
property of the dead (kin. This, however, is not agree¬ 
able to the opinions of the prefent phyfiologifts. The 
feElions of the arteries are circular, becaufe they are elaf- 
tic; and this is the reafon why, from the fmall arteries of 
the teeth, hemorrhagies are fometimes fatal. Tire aorta, 
indeed, of the thorax and abddmen, the carotids of the 
neck, and fome other arteries of the dead body, from their 
leflened extenlion, appear fomewhat flat or deprelfed ; but 
their round figure, or circular feCtion, is every where re- 
ftored by injeCtion. Their elafticity is alfo evident by that 
powerful compreffure, which a fegment of a large artery 
makes upon the finger that diftends it, and which is much 
ftronger in a dead than in a living body. In the living 
body, indeed, this force yields to that of the heart; but 
inftantly recovers itfelf when the heart is relaxed, and re- 
ffores the artery to its former diameter; and this makes 
the pulfe, which all arteries poflefs, although the fyftole 
and diaftole can be perceived by the finger only in the 
larger, not in the ('mailer ones. The Jlrengt/i of the arte¬ 
ries is confiderable enough: but as the denfe hard net¬ 
work of the outer cellular coat refufes to yield to a dif- 
tending force, it breaks without much difficulty, and al- 
moft eafier than tlie coats of the veins ; .and hence aneu- 
rifms ari(e. But, in general, the trunks are, in all parts 
of the body, weaker, and the branches ftronger in their 
coats ; whence the impulfe of the blood may exert a con¬ 
fiderable effeCl upon the former, but leaft of all on the ar¬ 
teries of the limbs. Hence it is-, that aneurifms are 1110ft 
frequently formed near the heart. 
Nature has difperfed the arteries through the whole ani¬ 
mal body, except in a few membranes where they have not 
yet been obferved. She hath difpofed of the trunks, every 
where, in places of fafety ; becaufe wounds in the (mailer 
trunks are always dangerous, and in the larger trunks fre¬ 
quently mortal. The (kin is fpread with numerous (hurt 
and fmall arterial branches; but the larger trunks, de¬ 
fended by the (kin and mufcles, creep along near the 
bones. In general, the arteries are in proportion to the 
parts of the body to which they are fent. The largeft go - 
to the fecretory organs, the brain, and fpleen; the (inaller 
ones to the mufcular parts. The extremities of the arte¬ 
ries, which are either cylindrical or nearly fo, fend off 
fmaller branches in greater abundance than the large arte¬ 
ries do, and thefe extremely fmall ramifications anaftomo- 
fing with one another form a kind of net-work ; as we fee 
more particularly in all membranes. By this means, tho* 
the paffage from the heart to any part of the artery is ob- 
ftruCted, the blood may nevertheless flow- through the ar¬ 
teries which are near the obftrudted one. Thus a gangrene 
or languor of the part is very ftrongly prevented, and the 
obftruftion is more ealily refolved by the repulfion of the 
obftacle into the larger part of the trunk. The lead arte¬ 
ries are either changed by a. continuation of their canals 
Vol. I. No. 40. 
625 
intoweins, or elfe a branch, fent out at right angles from 
the artery, is inferted by a like angle into a branch of fmall 
veins. Both thefe kinds of mechanifm are demonffrated to 
us by the microfcope, and the eafy return of. injections, 
through the veins into the arteries. A large artery is ne¬ 
ver oblerved to open into a vein. 
In the vifcera, we find the fmall arteries difpofed not fo 
much in net-work as in a fabric of a peculiar kind, wherein 
the fmall branches defcend very thick, or in chillers pa¬ 
rallel to the trunk, fo as to relemble brulhes, a variety of 
little trees or bodies, fmall ferpents, or threads, according 
to the various dil'pofition of the parts. Sometimes the ar¬ 
teries end in another maimer, namely, by being converted, 
into veifels of the fmaller kinds, which are continuous to 
the arteries, and indeed real arterial trunks; as may be ob¬ 
ferved in the ophthalmic artery, by tracing the arteries of 
the tunica choroides, or the colourlefs ones of the circle 
of the uvea and iris. In other places the fmaller vcftels 
feem to proceed laterally as branch.es from the trunks of 
the leaft fanguineous arteries; and thefe again are drawn 
out into trunks dill fmaller. Thefe are called excretory 
du£ls. It is with difficulty that thefe vcffels are filled with 
red blood ; of this, however, we have examples in the kid¬ 
neys, the liver, and the breads. Indeed the blood, when 
vitiated, penetrates the excretory duCts of the whole body, 
even without hurting the vefiels; nor is that aberration 
found to be productive of any evil conlequence after'the 
diforder of the blood is cured. 
Another termination of the arterial extremities is into 
the exhaling vefiels ; and this manner of their ending is 
very frequent in all parts of the body. The whole (kin, 
all membranes of the human body which form any clofe 
cavity, all the ventricles of the brain, the anterior and 
pofterior chambers of the eye, all the adipofe cells and 
pulmonary velicles, the whole cavity of the ftomach and 
inteftinal tube, and the trachea, are all of them repleniflied. 
with exhaling arteries of this kind. Thefe emit a thin, 
watery, gelatinous, humour, which, by congeftion, (tagna- 
tion, or excefs, is converted into a watery but coagulable 
lymph, as we fee in feveral difeafes, and in death. The 
exhalants are eafily demonftrable from the watery fweat. 
that enliies after injecting the arteries with any warm li T 
quor. In fome places they exhale indeed not a thin va¬ 
pour, but blood itfelf, as we fee in the heart, the'cellular 
fabric of the penis* urethra, clitoris, and nipple of the 
female bread ; in all which blood in its natural (late is 
poured out. 
The arteries, in a living perfon, are always full of blood ; 
fince the jet or dream from an artery is not interrupted 
by alternate flops, while the heart is inactive; but flows 
on in a continued thread. The microfcope alfo (hews the 
arteries, in living animals, to be full both in their fyftole 
and diaftole; nor can the circular fibres of the arteries fo 
far contract themfelves as entirely to evacuate thefe tubes. 
Every contraction of (he ventricle fends a new wave of 
blood into the arteries; this wave feldom exceeds two 
ounces, and confequently bears only a fmall proportion to 
the whole circulating mafs, yet it is fo forcibly, propelled 
by the heart as to drive the preceding waves before it. 
In eonfequence of this propuifion, the dimenfions of the 
cylindrical artery are augmented, the arterial coats are 
prelfed near each other, and the Terpentine flexures are 
confiderably increafed, as we often fee in injections. This, 
dilatation of the artery, whereby its capacity is changed 
from a lefs to a greater circle, is the pulfe, the diaftoje of 
which is an expanllon of the artery beyond its natural 
diameter. This attion is the charaCleriftic of life; it re- 
(ults from the heart only, and is in no wife natural to 
the arteries themfelves. Hence, when, the motion of the 
heart is intercepted, whether by aneurifrn, ligature, or 
othenvife, puliation of the arteries is to be felt ; and 
hence a fudden ceffatio'n of the pulfe, by a wound through 
the heart. The artery is proportionally more dilated, the 
more the velocity of the new wave exceeds that of the 
former one. 
7 U The. 
