460 THE BLOOD-VASCULAR SYSTEM. 



as the vestigial fold of Marshall. It is formed by the duplicature of the serous 

 layer over the remnant of the lower part of the left superior cava (duct of Cuvier), 

 which, after birth, becomes obliterated, and remains as a fibrous band stretching 

 from the left superior intercostal vein to the left auricle, where it is continuous with 

 a small vein, the oblique vein of Marshall, which opens into the coronary sinus. 



Surgical Anatomy. Paracentesis of the pericardium is sometimes required in cases of 

 effusion into its cavity. The operation is best performed in the fifth intercostal space, one incli 

 to the left of the sternum. The operation has been performed, however, in the fourth, sixth, 

 and seventh spaces, and also on the right side of the sternum. Porter considers that by "reason 

 of the uncertain and varying relations of the pleura, and also of the anterior position of the 

 heart, whenever the pericardial sac is distended with fluid, aspiration of the pericardium is a 

 much more dangerous procedure than open incision when done by skilled hands. ' ' He recom- 

 mends that the operation should be done by resecting the fifth costal cartilage on the left side. 

 By this means the surgeon avoids opening the pleural cavity, and secures continuous and free 

 drainage, if the case is one of purulent pericarditis. 



THE HEART. 



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

 lungs, and enclosed in the cavity of the pericardium. 



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

 or base, is directed upward, backward, and to the right, and corresponds with the 

 dorsal vertebrae, from the fifth to the eighth inclusive ; the apex is directed down- 

 ward, forward, and to the left, and corresponds to the space between the cartilages 

 of the fifth and sixth ribs, three-quarters of an inch to the inner side, and an inch 

 and a half below the left nipple, or about three and a half inches from the middle 

 line of the sternum. The heart is placed behind the lower two-thirds of the 

 sternum, and projects farther into the left than into the right half of the cavity 

 of the chest, extending from the median line about three inches in the former direc- 

 tion, and only one and a half in the latter ; about one-third of the heart lies to the 

 right and two-thirds to the left of the mesial plane. The anterior surface of the 

 heart is round and convex, directed upward and forward, and formed chiefly by the 

 right auricle and ventricle, together with a small part of the left ventricle. Its 

 posterior surface, which looks downward rather than backward, is flattened and 

 rests upon the Diaphragm, and is formed chiefly by the left ventricle. The right 

 or lower border is long, thin, and sharp ; the left or upper border short, but thick 

 and round. 



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. As has already been stated (page 455), the heart is sub- 

 divided by a muscular septum into two lateral halves, which are named respectively 

 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 

 ventricle. The course of the blood through the heart cavities and blood-vessels 

 has already been described (page 455). 



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

 surface. The groove separating the auricles from the ventricles is called the 

 auriculo-ventricular groove. It is deficient, in front, where it is crossed by the 

 root of the pulmonary artery. It contains the trunks 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 furrows, the inter ventricular grooves, which are situated 

 one on the anterior, the other on the posterior, surface ; these extend from the base 

 of the ventricular portion to near the apex of the organ ; the former being situated 



