514 



THE CIRCULATORY APPARATUS. 



and the pericardium is fixed to the sternum from the third rib to the xiphoid appendix, 

 as well as to the diaphragm. (The cartilage is not ossified until a late period.) 



In the Dog and Cat, the heart is oval or nearly globular. It is almost entirely resting 

 on the upper face of the sternum ; its anterior face has become the inferior, and its 

 point, directed backwards, touches the anterior surface of the diaphragm. The pericardium 

 is attached to the aponeurotic centre of the diaphragm. 



COMPARISON OF THE HEART OF MAN WITH THAT OF ANIMALS. 



The human heart is ovoid, and similar to that of the Carnivora ; the ventricular mass is 



not ocute at its apex, as in 



Fig. 265. Solipeds and Ruminants. Its 



direction is modified in conse- 

 quence of the antero-posterior 

 flattening of the chest. It is 

 situated across ihe median plane 

 of the thorax , its right face in 

 animals has become the anterior 

 face in Man, and is applied to the 

 sternum ; the anterior b( rder is 

 in him the right border, and the 

 posterior the left border. 



The organ is suspended ob- 

 liquely downwards, forwards, and 

 to the left ; consequently, the right 

 auricle is to the right of the 

 sternum, between the third and 

 fourth ribs, and the point on a 

 level with the sixth left inter- 

 costal space. The auricular ap- 

 pendages, particularly the right, 

 are more rounded and bulging 

 than in animals. The pulmonary 

 veins, four in number, open on 

 the upper face of the left auricle. 

 There are no essential dirtVr- 



enceg to be noted iu its j ntmial 



conformation. We may indicate 



HUMAN LUNGS AND HEART; FRONT VIEW. 



1, Right ventricle 2, Left ventricle ; 3, Right auricle ; 



m a y { ,lso mention the Thebesian 

 valve at the entrance of the coro- 



4, Left auricle ; 5, Pulmonary artery ; 6, Right the presence of a fold that passes 



pulmonary artery; 7, Left pulmonary artery; 8, from, the ring of Vieussens to the 



Ligament of ductus arteriosus ; 9, Arch of aorta; opening of the inferior vena cava : 



10, Superior vena cava ; 11, Arteria mnominata; 12, this is the Eustacliian valve. We 

 Right subclavian vein, with the artery behind it ; 

 13, Right common carotid artery and vein, 14, Left 



vena inuominata , 15, Left carotid artery and vein; nary vt in. 



16, Left subclavian vein and artery; 17, Trachea; The fibrous rings and muscular 



18, Right bronchus ; 19, Left bronchus ; 20, 20, fasciculi are disposed as in the 



Pulmonary veins ; 21, Superior lobe of right lung ; Horse. 



22, Middle lobe ; 23, Inferior lobe ; 24, Superior lobe The pericardium is a conical 



of left lung ; 25, Inferior lobe. sac; but instead of its base being 



presented upwards, it rests against 



the aponeurotic centre of the diaphragm ; its summit is lost among the large vessels, 



and it adheres to the posterior face of the sternum. 



