ANGEIOLOGY. 79 
nati, which leave between them deep interstices, in which the external and 
internal membranes of the heart come in contact. 
The right ventricle. This forms the greater part of the anterior surface 
of the heart, and is separated posteriorly from the left ventricle by a thick 
septum. The internal surface of the cavity of the right ventricle is covered 
by muscular fasciculi, known as the columne carne, some of them passing 
from one side to the other, and others contributing to the valvular arrange- 
ment between the right auricle and ventricle. These, called chorde tendinee, 
pass to the edge of the tricuspid valve, which arises from around the margins 
of the ostium, and projects into the cavity of the ventricle. 
The opening for the pulmonary artery is situated above the ostium veno- 
sum. It is round, and about an inch in diameter, and furnished with three 
valves, called semilunar and sigmoid, which are capable of completely 
closing this orifice, should the blood flow back from the pulmonary artery, 
but which lie close pressed to the sides when the current is in its normal 
direction. Through the pulmonary artery venous blood is carried to the 
lungs. 
The blood, after circulating through the lungs, is returned by the pulmo- 
nary veins into the left auricle, at the anterior inferior side of which is seen 
the left: auriculo-ventricular opening, or the communication with the left 
ventricle, about an inch in diameter. This, like the right auricle, is consti- 
tuted by a sinus venosus and auricular appendage. 
The left ventricle constitutes the principal bulk of the heart, and its walls 
are nearly three times as thick as those of the right ventricle. Its internal 
surface is roughened by the same columne carnez as the right. The ostium 
venosum, or opening between the left ventricle and auricle, is on the side 
also fortified by a valvular arrangement, the mztral valve, which prevents 
the reflux of blood. It is retained in the left ventricular cavity by chord 
tendinez. Close to the ostium is the opening for the aorta, guarded by 
three semilunar valves, very similar in arrangement to those of the pulmo- 
nary artery, being, however, stronger. 
Passage of blood through the heart. By the alternate contraction and 
dilation of the different chambers of the heart, the blood is caused to circu- 
late through it and the bloodvessels proceeding from it. The right and left 
ventricles contract, while the two auricles expand, and vice vers; contrac- 
tion of the ventricles being known as the systole, and their dilation the 
diastole. Commencing with the right side of the heart, we find that when 
the auricle contracts, the blood is forced towards the auriculo-ventricular 
opening, and backwards into the venz cave. The simultaneous expansion 
of the right ventricle, however, affords a free passage for the blood from 
the right auricle, which accordingly rushes through the ostium. The ven- 
tricle now contracting, forces the blood towards the ostium, and towards 
the’ pulmonary artery. Through the former it cannot pass, by reason of 
the tricuspid valve; and.as the'semilunar valves at the entrance of the pul- 
monary artery afford no impediment, the blood is drawn into the lungs. 
Simultaneously with this contraction of the ventricles, the right auricle 
dilates and becomes filled with fresh venous blood from the yen cave. 
ICONOGRAPHIC ENCYCLOPZDIA.—YOL, II. 50 785 
