218 



HUMAN PHYSIOLOGY 



a muscular cushion, the use of which will afterwards be 

 considered. 



Attachments and Relations of the Heart (Fig. 109). 

 The heart is attached, by the great vessels coming from it, 

 to the posterior wall of the chest at the level of the 5th 

 to the 8th dorsal vertebrae. Its plane of attachment faces 

 forwards and downwards. From this 

 the heart projects into the chest as a 

 conical mass downwards, forwards, and 

 to the left. It does not lie at right 

 angles to its plane of attachment, but, 

 when not contracting, it is limp and 

 hangs down, as shown in the diagram 

 (continuous line). Nor can it assume 

 a position at right angles to its plane 

 of attachment (dotted line), because the 

 front part of the heart lies against the 

 anterior chest wall over an area (the 

 prsecordium) bounded to the right by 

 the midsternal line, above by the fourth 



FIG. 109. Mesial Section i rv *u i i i_ *.i ^i i A. -i 



through the Thorax to left rib > below b y the seventh left rib, 

 show the attachment and to the left by a vertical line inside 

 the nipple line. 



From the oblique position of the 

 heart, it is the right side auricle and ventricle which is 

 directed forwards, and it is a portion of the right ventricle 

 which lies in relationship with the chest wall. The rest of 

 the organ is covered by the lungs. The only parts of the 

 left side which can be seen from the front are the tip of 

 the left auricular appendix, and a narrow strip of the left 

 ventricle. 



Below and behind the heart lies upon the central tendon 

 of the diaphragm to which the pericardium is attached. 



All round it are the lungs completely filling up the rest of 

 the thorax. 



The heart is enclosed in a strong fibrous bag, the Peri- 

 cardium, which supports it and prevents over-distension. 

 When fluid accumulates in this bag the auricles are pressed 

 upon and the flow of blood into them is impeded. 



and relations of the 

 Heart. 



