- A, inferior constrictor muscle (aids in conveying food down the œsophagus);
- B, œsophagus;
- C, section of the right bronchus;
- D, two right pulmonary veins;
- E, great azygos vein crossing œsophagus and right bronchus to empty into the superior vena cava;
- F, thoracic duct;
- H, thoracic aorta;
- K, lower portion of œsophagus passing through the diaphragm;
- L, diaphragm as it appears in sectional view, enveloping the heart;
- M, inferior vena cava passing through diaphragm and emptying into auricle;
- N, right auricle;
- O, section of right branch of the pulmonary artery;
- P, aorta;
- R, superior vena cava;
- S, trachea.
The valve on the right side is called the tricuspid, because it consists of three little folds which fall over the opening and close it, being kept from falling too far by a number of slender threads called chordæ tendinæ. The valve on the left side, called the mitral, from its fancied resemblance to a bishop’s mitre, consists of two folds which close together as do those of the tricuspid valve.
The slender cords which regulate the valves are only just long enough to allow the folds to close together, and no force of the blood pushing against the valves can send them farther back, as the cords will not stretch The harder the blood in the ventricles pushes back against the valves, the tighter the cords become and the closer the folds are brought together, until the way is completely closed.
From the right ventricle a large vessel called the pulmonary artery passes to the lungs, and from the left ventricle a large vessel called the aorta arches out to the general circulation of the body. The openings from the ventricles into these vessels are guarded by the semilunar valves. Each valve has three folds, each half-moon-shaped, hence the name semilunar. These valves, when shut, prevent any backward flow of the blood on the right side between the pulmonary artery and the right ventricle, and on the left side between the aorta and the left ventricle.
Fig. 71.—Right Cavities of the Heart.
- A, aorta;
- B, superior vena cava;
- C, C, right pulmonary veins;
- D, inferior vena cava;
- E, section of coronary vein;
- F, right ventricular cavity;
- H, posterior curtain of the tricuspid valve;
- K, right auricular cavity;
- M, fossa ovalis, oval depression, partition between the auricles formed after birth.
186. General Plan of the Blood-vessels Connected with the Heart. There are numerous blood-vessels connected with the heart, the relative position and the use of which must be understood. The two largest veins in the body, the superior vena cava and the inferior vena cava, open into the right auricle. These two veins bring venous blood from all parts of the body, and pour it into the right auricle, whence it passes into the right ventricle.
From the right ventricle arises one large vessel, the pulmonary artery, which soon divides into two branches of nearly equal size, one for the right lung, the other for the left. Each branch, having reached its lung, divides and subdivides again and again, until it ends in hair-like capillaries, which form a very fine network in every part of the lung. Thus the blood is pumped from the right ventricle into the pulmonary artery and distributed throughout the two lungs (Figs. [86] and [88]).