302 



THE HEART. 



EXTERNAL FORM OF THE HEART. 



The heart is a hollow muscular organ, divided by a longitudinal septum 

 into a right and a left half, each of which is again subdivided by a transverse 

 constriction into two compartments, communicating with, each other, and 

 named auricle and ventricle. Its general form is that of a blunt cone, flattened 

 on its under surface. The broader end, or base, by which it is attached, is 

 directed upwards, backwards, and to the right, and extends from the level 

 of the fourth to that of the eighth dorsal vertebra. The apex is turned 

 downwards, forwards, and to the left, and corresponds in the dead body with 

 the cartilage of the sixth rib. In the living subject its stroke against the 

 walls of the chest is felt in the space between the cartilages of the fifth and 

 sixth ribs, a little below and within the left mammilla. The heart, there- 

 fore, has an oblique position in the chest, and besides this is n on symmetrically 

 placed, as it projects farther into the left than into the right half of the 

 thoracic cavity, passing on an average about an inch or an inch and a half 

 beyond the middle line in the one direction, and upwards of three inches 

 in the other. Its position is affected more or less by that of the body ; 

 thus it comes more extensively into contact with the anterior walls of the 



Fig. 227. 



Fig. 227. VIEW OP THE HEART AND 

 GREAT VESSELS FROM BEFORE (from R. 

 Quain). 



The pulmonary artery has been cut short 

 close to its origin in order to show the first 

 part of the aorta. 1, anterior part of the 

 right ventricle ; 2, left ventricle ; 3, root of 

 the pulmonary artery ; 4, ascending part of 

 the arch of the aorta ; 4', the posterior or 

 descending part of the arch ; between these 

 is seen the transverse or middle part from 

 which the brachio-cephalic arteries take their 

 origin ; 4", the descending thoracic aorta ; 

 5, the appendix and anterior part of the 

 right auricle ; 6, those of the left auricle ; 

 7, the right, and 7', left innominate or 

 bracbio-cephalic veins joining to form the 

 vena cava superior ; 8, the inferior vena 

 cava below the diaphragm ; 9 one of the 

 large hepatic veins ; +, placed in the right 

 auriculo-ventricular groove, points to the 

 right or posterior coronary artery ; + + , 

 placed in the anterior interventricular 

 groove, points to the left or anterior coronary 

 artery. 



chest when the body is in the prone 

 posture or lying on the left side. 

 In inspiration, on the other hand, 

 when the diaphragm sinks and the 

 lungs expand, its apex is withdrawn 

 from the thoracic parietes. 



At its base the heart is directly attached to the great blood-vessels, and 

 it is also connected with them by the serous layer of the pericardium, 

 which passes from tho one to the other. In the remainder of its extent the 

 heart is entirely free, and movable within the sac of the pericardium. The 



