PHYSIOLOGICAL ANATOMY OF THE HEART 



33 



Physiological Anatomy of the Heart. The heart of the human sub- 

 ject is a pear-shaped muscular organ, situated in the thoracic cavity Jts 

 base lying in the median line and its apex at the fifth intercostal space, 

 three jnches (7.6 centimeters) to the left of the median line, OL_one inch 

 (2.5 centimeters) within the line of the left nipple. The weight of the 

 heart is ten to twelve ounces (283 to 340 grams) in the male, and eight 

 to ten ounces (227 to 283 grams) in the female. It has four distinct 

 cavities, a right and a left auricle and a right and a left ventricle, the 

 ventricles being the more capacious. The heart is held in place by the 

 attachment of the great 

 vessels to the posterior 

 wall of the thorax ; while 

 the apex is free and is 

 capable of a certain ex- 

 tent of movement. The 

 entire organ is enveloped 

 in a fibrous^sac ^called 

 the pericafdium. This 

 sac is lirfed~witlTa serous 

 membrane, which is at- 

 tached to the great ves- 

 sels at the base and is 

 reflected over the sur- 

 face of the heart. This 

 membrane is lubricated 

 with about a drachm 

 (3.7 cubic centimeters) 

 of liquid, so that the 

 movements of the heart 

 are attended with but 

 slight friction. The se- 

 rous pericardium does not present any differences from serous mem- 

 branes in other situations, which form a part of the great lymphatic 

 system. The cavities of the heart are lined with a smooth membrane, 

 called the endocardium, which is continuous with the lining membrane 

 of the bloodvessels. 



The right auricle receives the blood from the venae cavae and empties 

 it into the right ventricle. The auricle consists of a principal cavity, or 

 sinus, as it is called, with a little appendix, called, from its resemblance 

 to the ear of a dog, the auricular appendix. It presents two large open- 

 ings, for the vena cava ascendens and the vena cava descendens respec- 

 tively, with a small opening for the coronary vein. It also has another 



Fig. 16. Heart in situ (Dalton, in Flint, On the Heart) . 



a, b, c, d, e, ribs ; i, 2, 3, 4, 5, intercostal spaces ; vertical line, 

 median line ; triangle, superficial cardiac region ; x on the fourth 

 rib, nipple. 



