104 



ANATOMY FOK NUKSES. 



[CHAP. IX. 



other. Its general form is that of a blunt cone. It is situated 

 in the thorax, between the lungs, and, together with the adja- 

 cent parts of the great blood-vessels which carry blood to and 

 from it, is enclosed in a membranous covering, the pericardium. 



The heart lies nearer 

 to the front than to 

 the back of the chest, 

 and is placed behind 

 the sternum and the 

 costal cartilages, the 

 broader end or base 

 being directed up- 

 wards, backwards, and 

 to the right, while the 

 pointed end or apex 

 points downwards, for- 

 wards, and to the left. 

 The impulse of the 

 heart against the w^all 



FIG. 78. -THE HEART AND LUNGS, l, right ven- f f i i , f ,, . 

 tricle; 3, right auricle; 6, 7, pulmonary artery; 9, ( 

 aorta; 10, superior vena cava; 11, innominate ar- the Space between the 



i fu 



a 



tery; 12, right subclavian vein ; 14, innominate vein ; 



15, left common carotid; 17, trachea; 20, pulmonary 



veins ; 22 to 25, lungs, partially turned back to show little below and to the 



veins on left side. 



inner side of the left 



nipple. It has, therefore, a very oblique position in the chest. 

 It is suspended and kept in position by the great vessels at the 

 base, and is also supported by the diaphragm. According to 

 Laennec, the heart in its normal condition is about equal in 

 size to the fist of the individual to whom it belongs. 



The main substance of the heart is composed of muscular 

 tissue. Between the muscle fibres is a certain amount of in- 

 terstitial tissue with numerous blood-vessels and lymphatics, 

 and, in some parts, nerves and ganglia. There is also a consid- 

 erable amount of fat, chiefly collected at the base of the heart, 

 and beneath the pericardium. The muscular tissue of the heart 

 differs from all other involuntary muscular tissue in possessing 

 transverse striae. The fibres continually branch and unite with 

 one another so as to form a kind of network or sponge-like sub- 

 stance. The arrangement of the fibres differs in the auricles 

 and the ventricles, and is very intricate; the fibres run trans- 



