HEAR %. 
neral veins ; and their mast reg in the liver goon no pecu- 
not anaftomofe circum- 
n the general fy Hence there is 
no neceffity for naitbinanfans as in ee inne fpleen, kidney, 
In the hepatic portion of the fyttem the communica- 
‘ous, as the courfe of the blood is 
The circus 
orrhoidal veins, which, by their pofi- 
tion’ are ahold ‘isied to this influence, are the moft fre- 
- quently varicous. 
Whether this fyftem communicates with the former, in its 
minute branches, is not yet afcertained. 
Many authors, and pelea s Haller, confidering that 
em mpulfion, have afcribed to the 
vellels a fuperior degree of frcngth the ftruéture in 
reality appears the fame. The exittence of fibres is dubious. 
In the hepatic part of the veffels thege is a greater abundance 
of cellular tiffue ae, ally. 
The analogy vg Sg in the abdominal ae general 
fyftems of Pick blood, leads us naturally to a cor- 
refponding refemblance in their vital eres, = SE ae 
oat Imitation of the mefenteric veins has precifely the 
eis as that of any others in the general fyftem. 
The common membrane of the vena portarum is every where 
deftitute of valves. be the courfe of the blood is fo much 
fhorter in this inftance, there is the lefs need of providin 
the fupports farnifhed by thofe folds: and the abfence o; 
an organ of impulfion is attended with a want of the re 
flux obferved in the other veins, fo that the fluid runs ieays 
‘uniformly j in this fyftem from one fet of ‘capillaries to the 
ty without any seireiends paflage. 
« This a >” fays Bichat, « de ends alfo in part on 
Ba aga y,”” fays P P 
ver prefents to the 
f thofe obitacles api rege ccur fo fre- 
art 
on Bloda.: iinelien: the ao iehons 
e inthe courfe of the blood in the 
3 Qo 
oO 
arteries, where the action of the heart Scape the whole 
effe&. There is much obfcurity in this fubje€t, as well as 
general veins, and every 
judicious mind cannot fail to obferve that there is a great 
vacuum to be filled up in both cafes. 
In the abdominal, as in the general venous fyftem, e xter- 
nal forces produce “conliderable effe he motions of the 
refpiratory mnufcles, the dilatation and contraction o the » 
hollow vifcera, the locomotion of t e moveable abdominal 
with the 
perpendicular polition, to retard the blood’s courfe in he 
hemorrhoidal veins, and thereby to occafion varices. Y 
extent of thi8 influence is —— by 
he reprefents et the circulation cannot (a 
out it. e blood is fill seiadhidiees to the liver, 
ie the abdoeatin 4 is laid open in a living animal; but this 
circulation is eg weakened i in a fhort time, before the 
general is even lan 
The abdominal aot of black blood is not ifolated in 
the foetus; it forms one with the two others, through the 
communication of the canalis venofus: hence the feetus has 
a tingle vafcular fyftem, while the infant Saat has breathed 
ie 
pofleiles three feparate fyftems, two of re one Shes 
red bloo . The mode, in which the two 
cate in the liver of the tin had been 2 ytens co Srecery Fy 
the article Empryo. abdominal parsed fyftem is ‘lef 
developed at this time, ‘hin 4 in the fequel ; 
much larger on account of the blood, bande arrives -at it 
from the placenta through the sibilities vein. The excels 
of {ize in the liver is the more ftrongly mar propor- 
tion as the foetus is younger; and this pre brute oe accord+ 
ing to Portal, continues till the feventh month. e 
tion arifes whether they are of the 
fubje& we have no data to form a judgment. 
of birth, the fupply of — Lhe the umbilical vein is cut 
and the liver is bloo 
jot of black pias is cut sll: sin hat the sal ad gee 
bulk of the liver is diminifhed. ‘hus the latter organ ex- 
periences changes at this time, which are exactly the inverfe — 
of thofe that occur in the Jung. of youth, 
the abdominal {yftem, like ne general, is not ina ftate of 
s ecuet activity ; it is called into greater exertion towards the 
interval between the thirtieth and fortieth years. That is 
the age of teen difeafes, of hemorrhoids, « and = hypo. 
ndriac a 
i ections, which are 
of the liver. in oo age, like ie sein 
fyftem ; nor : oeabibie bony depofitions. 
Of the Ca —It mutt appear evident, from 
‘delcription ae there are two of thefe, per- 
feétly ceding One, generally difperfed 
over the whole body, plicit all the vifcera and organs 
confiderably in this » and of every defcription, is the feat of the change of t 
fequently may be more or lefs from red to black; while, in the other, which is concen- 
-ording as the paflage t the trated in the lungs, the blood is i convert black 
gh bie. been bal oe more i tes Tet tored. ‘The circ nee whic — dabulans our . 
Ae mechanifm of t Sircitalian the minal portion notice i the capillary fyftem, are, rit, that citculation 
bat iy frtem is exadt iy the fae st ‘the general veins: in them is” et 4 8 oem laws; 2dly, that moit of 
nny. ~ "saa part is unique ti the antinakecuneS the the important. nétions of the organic life, = ( th 
Vou XVI XVIL ne analogy to the courhe af the blood in the nutrition, exhalation, &c. take place in ; 3dly, a 
af 
att 
