THE HEART. 



1087 



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

 a half in breadth in the 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 proportions 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 subdivides each half of the organ into two 

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

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



Bristle passed through 

 Right Auriculo- Ventricular opening. 



FIG. 695. The right auricle and ventricle laid open, the anterior walls of both being removed. 



dark venous blood from the entire body, by the superior and inferior vena cava 

 and coronary sinus. From the right 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. 



The great transverse groove separates the auricles from the ventricles, and is 

 called the auricula-ventricular groove. It is deficient, in front, from being crossed 

 by the root of the pulmonary artery. The two ventricles are also separated from 

 each other on the surface by two longitudinal furrows, the interventricular grooves, 

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

 tend from the base of the ventricle to a little to the right of the apex of the organ, 

 where they are continuous, 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, while the apex is made up entirely of the left ventri- 



