” . * bllial = z ra y 
+ ‘ 9 : a 4 
: : Le PRENERIOMY ER Sl 69 
again to the auricles. The blood is brought from every of the 
body to the heart by the two cave veins, which terminate ie the right 
auricle. ‘I'he right auricle, when distended with blood, contracts 
and empties itself into the right ventricle : the right ventricle then 
_ contracts, and propels the~ blood into the Jung artery, the opening 
between the ventricle and auricle being shut by the three pointed 
valves. ‘The lung artery conveys the blood by its numerous rami- 
fications into the small branches of the air cells of the lungs, where 
it undergoes a change, and passes into the veins, which bring it, by 
four trunks, into the left auricle of the heart. It is prevented 
returning from the lung artery into the right ventricle, by the half 
moon valves, which are placed at its origin. The blood having thus 
ya through the lungs, and become of a florid, bright red color, 
istends the left auricle, which is then stimulated to contraet, and 
pours the blood into the left ventricle. This ventricle next contracts 
and propels the blood through the fountain, to be conveyed by its 
branches to every part of the body. The valves at the auricular 
opening into the left ventricle, prevent the blood from returning 
when the ventricle contracts, into the auricle ; and lest the blood 
should be prevented by any impediments from passing immediately 
along the fountain, the three half-moon valves, placed at its origin, 
prevent its regurgitating into the yentricle. From the numerous 
arteries of the fountain the blood is conveyed into the veins, where 
it loses its florid color,and becomes darker, to be returned in the _ 
way above mentioned, to the right auricle. Thus the blood of the 
right auricle and ventricle, and of the lung arteries, is of a dark color; — 
and that of the lung veins, left auricle, ventricle, and all the arteries, 
(except the lung,) of a bright red hue. — 
From what has been said, it is evident that the action of the 
heart consists in the alternate contraction and dilatation of its auri-° 
cles and ventricles. The excessive sensibility of the membrane 
which lines the auricles and ventricles disposes them to contrac- 
tion, which is effected by the irritation and stimulus of the blood, and. 
by that of the distension of its cayities, 
OF THE ABDOMEN. 
. : eee ee 
A cavity situated between the chest and pelvis, and divided into 
several regions, as has been already mentioned. The external parte 
are, the skin, five pair of abdominal muscles, and the lining mem- — 
brane. The internal parts, or viscera, are, the caul, stomacli, 
small, and large intestines, liver, gall-bladder, mesentery, milk ves- 
sels, spleen, pancreas, kidneys, upper kidney glands, descending 
fountain, and ascending cave vein. = Se 3 it 
.. THE LINING MEMBRANE. 
