HEART. 757 



and inferior vena cava and the four pulmonary veins. Its inner surface is 

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

 movements of the heart. 



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 vertebra : the apex is directed for- 

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

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

 left nipple. The heart is placed behind the lower two-thirds of the sternum, 

 and projects further into the left than into the right cavity of the chest, extend- 

 ing 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 carti- 

 lages ; 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 point above men- 

 tioned, as the situation of 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, 

 and is formed chiefly by the left ventricle. 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 ; this 

 increase 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 vena 

 cava, 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 distributed, by the aorta and its subdivisions, through the 

 entire body. This constitutes the circulation of the blood in the adult. 



This division of the heart into four cavities is indicated by grooves upon its 

 surface. The great transverse groove separating the auricles from the ventri- 

 cles, 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 the anterior, the other on the 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, 



