SECTION IX 







HEART AND BLOODVESSELS OF HEAD, NECK AND TRUNK 



The Heart. 



THE Heart is a four-chambered muscular organ situated in 

 the thorax, in the space between the lungs, and resting on the 

 diaphragm. Its function is to receive the blood from the veins 

 and to propel it through the arteries. 



The shape of the heart is that of a cone ; it has an apex, a 

 base, and two surfaces (inferior and antero-superior) . A shallow 

 groove runs round the heart transverse to its long axis, sepa- 

 rating the upper auricular portion from the lower ventricular 

 portion. The division of the upper portion into two auricles is 

 only faintly marked, but a distinct groove divides the lower 

 portion into two ventricles. 



The heart is enclosed in a fibro-serous sac the pericardium 

 which separates it from the surrounding organs. It rests on 

 the diaphragm, the long axis pointing obliquely downwards,, 

 forwards, and to the left. On the surface of the body its position 

 is marked by a quadrilateral area, the boundaries of which are 

 as follows : 



Eight side a line slightly convex outwards from the upper 

 end of the third costal cartilage to the sixth, its greatest 

 distance from the middle line being 1| inches. 



Base from the lowest point on the right side to the fifth in- 

 tercostal space on the left side, 3J inches from the middle line. 

 This point marks the position of the apex of the heart. 



Left side a line slightly convex outwards from the left ex- 

 tremity of the base line to the lower border of the second inter- 

 space on the left side, 1 inch from the mid-line. 



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