HEART. 
this fyftem, where there is no impelling ‘power, as in the ar- 
ch an obftacle.?’ 
into a certain ee 
of trunks, opening into thofe which terminate in the t 
auricle of the heart: thefe are the internal jugular, “tab. 
clavian, and azygos veins sors and the iliac below. Like 
_ the arterial trunks, they are placed deeply, and proteéted 
the furrounding organs from external i injury, fince a 
wound might produce fatal hemor rhage. 
No conttant rule is obferved as te fize, i in the union of the 
niargetrunks. The angles 
of junction var Y, being Cretinee right and fometimes 
obtufe, but moft frequently acute.‘ In the diftribution and 
number of thefe veffels,”’ fays Haller, “ there is ae more 
variety than in the arteries ; and fo inconftant are 
rangements of nature in this fyftem, that, age, T ae 
profecuted the courfe of the arteries enw. in all parts of 
the body, I could never undertake abour of a fimilar 
inguiry into the diftribution of the veins. It would be ne- 
celfary to give almoit as many ee as there are fub- 
jects; fuch at leaft would be the a the extremities, 
ec e, head, and neck, while their gt in the vifcera is 
tolerably Pegas and i that of the arteries.’’. Elem. Phy- 
fiol, lib. 2 2, fe 
A vein is cy lade when examined in a part where it 
receives no branch. appears flattened on the dead body, 
fince its hee are collapled in confequence of the erase © of « 
bleod: but if it be diftended, it regains its original fo 
Tn the living fubje& the form of the veins is roun 
vein, traced from the extremity of the body to the heart, i is 
eH gs oft naire 
veins; {mall 
conical, with the bafis of the cone at the heart, and its pe 
very much lefs fs than the fum 
branches, we fhall find that the fame comparing holds good 
of the vena cava and its branches. fays that he 
finds the ratios of the trunks to the fae to be nearly 
the fame as in the arterial fyftem. Bichat ftates that the 
Seager are not fo conftant as in the arteries: that the 
of the branches, in certain inftances, far exceeds the 
He refers this, 
hen; and 
. when a 
in ftanding, the sae 
e relation o he trunks to the a hoes 18 
te all attempts at exact. 
to any ufeful refult. 
[he veins communicate together more freely than the ra 
inte {maller ramifications the me pies are f 
ee to form a real network : they ar 
ly fewer in the fucceeding branches, and acid ‘ipl Hequent 
bot 
teries, In 
numerous 
of “te united areas of all its. i 
cafions. 
| Seti of gravitation, w 
parative. ed on movin 
as we proceed towards the heart. Yet we ftill find many 
even in the large branches, and in this refpe& the veins are 
tara ap neuies from the arteries, the larger trunks 
of which are alm oft always ifolated: Thefe anaftomofes 
unite, ina Vv 
feated veins : 
t 
pig are joined together, under the angle of the jaw, 
a large branch ; the batilic, cephalic, ane: ges nume= 
ef divitions {pread over the forearm, to the brachial, 
radial, and ulnar, by feveral branches penetrating between 
the mufcles ; ; ‘and the faphene to the crural and pe- 
Thus commoanicaltoes be- 
oduced by exerting the mufcles 
or the continuation of the circulation, when the fuperfi - 
cial veins are com 
e are indlaiesds according 
to _Bichat, yh the Solas ot following various —_ sin 
iSTfa 
ral the anafta 
more nie dilated in the 
great difficulty which the blood experiences in afecnding 
contrary to its own weight. 
A comparative view of the courfe of the blood in seo 
two fyftems will fhew us, perhaps, that there are mean 
explaining why the communications are more frequent in ae 
venous than in the arterial fyflem. The _— blood is ma- 
nifeftly influenced by the force of gravita 
The ere& —_ occafion: 
ulaly aft 
s the res "of the leiie 
vi 
will affeét its courfe; and to” ‘this 
‘a caufe we may perhaps afcribe the peculiar effe 
the — poe ar in the circular dsetiica. 
ges. tae and various: mechanical 
L2 caufes, 
‘External 
