HEART. 691 



and glistening, and secretes a thin fluid, which serves to facilitate the movements 

 of the contained organ. 



The arteries of the pericardium are derived from the internal mammary, the 

 bronchial, the cesophageal, and the phrenic. 



THE HEART. 



The Heart is a hollow muscular organ, of a conical form, placed between the 

 lungs, and inclosed in the cavity of the pericardium. 



Position. The heart is placed obliquely in the chest ; the broad attached end 

 or base is directed upwards and backwards to the right, and corresponds to the 

 interval between the fifth and eighth dorsal vertebrae ; the apex is directed for- 

 wards and to the left, and corresponds to the interspace between the cartilages of 

 the fifth and sixth ribs, one inch to the inner side, and two inches below the left 

 nipple. The heart is placed beneath the lower two-thirds of the sternum, and 

 projects further into the left than into the right cavity of the chest, extending 

 from the median line about three inches in the former direction, and only one and 

 a half in the latter. Its upper border would correspond to a line drawn across 

 the sternum, on a level with the upper border of the third costal cartilages ; and 

 its lower border, to a line drawn across the lower end of the gladiolus, from the 

 costo-xiphoid articulation of the right side, to the part corresponding to the apex. 

 Its anterior surface is rounded and convex, directed upwards and forwards, and 

 formed chiefly by the right ventricle and part of the left. Its posterior surface is 

 flattened, and rests upon the Diaphragm. The right border is long, thin, and 

 sharp ; the left border short, but thick and round. 



Size. The heart, in the adult, measures about five inches in length, three inches 

 and a half in breadth in its broadest part, and two inches and a half in thickness. 

 The prevalent weight, in the male, varies from ten to twelve ounces, in the 

 female, from eight to ten ; its proportion to the body being as 1 to 169, in males, 

 1 to 149 in females. The heart continues increasing in weight, and also in length, 

 breadth, and thickness, up to an advanced period of life ; and this is more marked 

 in men than in women. 



Component parts. The heart is subdivided by a longitudinal muscular septum, 

 into two lateral halves, which are named respectively, from their position, right 

 and left ; and a transverse constriction divides each half of the organ into two 

 cavities, the upper cavity on each side being called the auricle, the lower the 

 ventricle. The right is the venous side of the heart, receiving into its auricle the 

 dark venous blood from the entire body, by the superior and inferior venae cavae, and 

 coronary sinus. From the auricle, the blood passes into the right ventricle ; and 

 from the right ventricle, through the pulmonary artery, into the lungs. The 

 blood, arterialized by its passage through the lungs, is returned to the left side of 

 the heart by the pulmonary veins, which open into the left auricle ; from the left 

 auricle the blood passes into the left ventricle, and from the left ventricle is dis- 

 tributed, by the aorta and its subdivisions, through the entire body. This con- 

 stitutes the circulation of the blood in the adult. 



This, division of the heart into four cavities is indicated upon its surface in the 

 form of grooves. Thus, the great transverse groove separating the auricles from 

 the ventricles is called the auriculo-ventricular groove. It is deficient, in front, 

 from being crossed by the root of the pulmonary artery, and contains the trunk 

 of the nutrient vessels of the heart. The auricular portion occupies the base of 

 the heart, and is subdivided into two cavities by a median septum. The two 

 ventricles 'are also separated into a right and left, by two longitudinal furrows, 

 which are situated, one on its anterior, the other on its posterior surface ; these 

 extend from the base to the apex of the organ, the former being situated nearer 

 to the left border of the heart, and the latter to the right. It follows, therefore, 

 that the right ventricle forms the greater portion of the anterior surface of the 

 heart, and the left ventricle more of its posterior surface. 



