Part 22 (1/2)

333. The CIRCULATORY ORGANS are the _Heart_, _Arte-ries_, _Veins_, and _Capil-la-ries_.

334. The HEART is placed obliquely, in the left cavity of the chest, between the right and left lung. Its general form is that of an inverted cone, the base of which is directed upward and backward, toward the right shoulder, while its apex points forward to the left side, about three inches from the sternum to the s.p.a.ce between the fifth and sixth ribs. Its under side rests upon the tendinous portion of the diaphragm. The heart is surrounded by a sac, called the _per-i-cardi-um_, (heart-case.) The interior surface of this membrane secretes a watery fluid, that lubricates the exterior of the heart, and obviates friction between it and the pericardium.

331. what is the ultimate object of the food? 332. Of what is the blood composed? What is said of the distribution of the blood? 333.

Name the circulatory organs. 334-351. _Give the anatomy of the circulatory organs._ 334. Describe the heart.

[Ill.u.s.tration: Fig. 66. A front view of the heart. 1, The right auricle of the heart. 2, The left auricle. 3, The right ventricle. 4, The left ventricle. 5, 6, 7, 8, 9, 10, The vessels[13] through which the blood pa.s.ses to and from the heart.]

[Ill.u.s.tration: Fig. 67. A back view of the heart. 1, The right auricle.

2, The left auricle. 3, The right ventricle. 4, The left ventricle. 5, 6, 7, The vessels that carry the blood to and from the heart. 9, 10, 11, The nutrient vessels of the heart.]

[13] All vessels that carry blood to the heart, are called _veins_.

All vessels that carry blood _from_ the heart, are called _arteries_.

With what is it surrounded? What is its use? How much fluid does this membrane contain when healthy?

_Observation._ In health, there is usually about a tea-spoonful of fluid in the pericardium. When these parts are diseased, it may be thrown out more abundantly, and sometimes amounts to several ounces, producing a disease called dropsy of the heart. But all the unpleasant sensations in the region of the heart are not caused by an increased amount of fluid in the pericardium, as this disease is not of frequent occurrence.

335. The heart is composed of muscular fibres, that traverse it in different directions, some longitudinally, but most of them in a spiral direction. The human heart is a double organ, or it has two sides, called the right and the left. The compartments of the two sides are separated by a muscular _septum_, or part.i.tion. Again, each side of the heart is divided into two parts, called the _Auri-cle_ (deaf ear) and the _Ventri-cle_.

[Ill.u.s.tration: Fig. 68. A section of the heart, showing its cavities and valves. 3, The right auricle. 4, The opening between the right auricle and right ventricle. 5, The right ventricle. 6, The tricuspid valves. 7, The pulmonary artery. 9, The semilunar valves of the pulmonary artery.

10, The septum between the right and left ventricle. 12, The left auricle. 13, The opening between the left auricle and left ventricle. 14, The left ventricle. 15, The mitral valves. 16, The aorta. 17, The semilunar valves of the aorta.]

336. The AURICLES differ in muscularity from the ventricles. Their walls are thinner, and of a bluish color. These cavities are a kind of reservoir, designed to contain the blood arriving by the veins.

337. The VENTRICLES not only have their walls thicker than the auricles, but they differ in their internal structure. From the interior of these cavities arise fleshy columns, called _co-lumn carne-_. The walls of the left ventricle are thicker and stronger than those of the right.

335. Of what is the heart composed? Give its divisions. 336. Describe the auricles. 337. Describe the ventricles.

338. The cavities in the right side of the heart are triangular in shape; those of the left, oval. Each cavity will contain about two ounces of blood. Between the auricle and ventricle in the right side of the heart, there are three folds, or doublings, of thin, triangular membrane, called the _tri-cuspid_ valves. Between the auricle and ventricle in the left side, there are two valves, called the _mitral_. There are seen pa.s.sing from the floating edge of these valves to the column carne, small white cords, called _chord tendi-n_, which prevent the floating edge of the valve from being carried into the auricle.

339. The right ventricle of the heart gives rise to the _Pulmo-na-ry_ artery; the left ventricle, to a large artery called the _A-orta_. At the commencement of each of these arteries there are three folds of membrane, and from their shape, they are called _sem-i-lunar_ valves.