THE PEEICABDIXJM AND HEART 



743 



wUi, ^^ °'l^'' ?^ contact of the pericardium with the chest wall is chiefly ventral, and is best seen 

 muscles) TheT,l^'^,'tpH?f 'k ^", ^^is position (after removal of the mtercostal and rectus thorac^ 

 muscles) the aiea is seen to be a.lmost triangular. The anterior border of the triangle (formed by 



Xe"^ e^d no'nf ttfthfw ^"^^ f ^^.^"^ "^^^ fourth costal cartilage and extends across the median 

 plane endmg at the third interchondral space near the costo-chondral junction. The right border 

 berinf/tTe lpf?pnT^lTv,^ °^ the fourth rib to the eighth chondro-sternal joint. The fef border 

 begins at the left end of the anterior border, crosses the fourth cartilage nearly an inch from its 

 junction with the rib and the fifth and sixth chondro-costal junctions. 



The heart differs greatly in form and position from that of the larger animals. 

 In diastole it is ovoid and the apex is blunt and rounded. Its long axis is very 

 oblique. Thus the base faces chiefly toward the thoracic inlet and is opposite to 

 the ventral part of the third rib. The apex is on the left side at the sixth inter- 

 chondral space or seventh costal cartilage, and in close relation to the sternal part 

 of the diaphragm. The stemo-costal surface corresponds largely to the floor of 

 the thorax from the fifth chondro-sternal joint backward. It is crossed obliquely 



Aorta 



Left pul- 

 monary 

 artery 



Pulmonary veins 



Left brachial 

 artery 



Brachiocephalic 

 artery 



Anterior venn - 

 cava 



Right auricle 



Pulmonary artery 

 Conus arteriosus 



Right ventricle 



Posterior vena cava 



Left ventricle 



1, Pulmonary veins; 



Apex 



Fig. 612. — Heart of Dog; Left View. 

 , left auricle; 3, vessels and fat in coronary groove; 4, vessels and fat in left or ventral longitu- 

 dinal groove; o, vessels and fat in intermediate groove. 



by the left (or ventral) longitudinal groove, which begins behind the origin of the 

 pulmonary artery, and joins the right (or dorsal) groove at the right border, thus 

 forming a notch not far from the apex. The diaphragmatic surface is less ex- 

 tensive and less convex. On it is the right (or dorsal) longitudinal groove, which 

 begins at the coronary groove just behind the termination of the posterior vena 

 cava and joins the left (or ventral) groove to the right of the apex. There is fre- 

 quently an intermediate groove between these on the left ventricle, which extends 

 a variable distance toward the apex. The weight of the heart of a dog of medium 

 size is five to six ounces, and is about 1 per cent, of the body weight. 



The relative weight is subject to wide variation. It is large in hunting dogs and such as are 

 trained for speed or worked. In fat dogs of sedentary habit it may be only about 0.5 per cent. 



The fossa ovalis is very shallow and is bounded in front by the intervenous crest. The musculi 

 pectinati form a rich network in the right auricle. The tricuspid valve has two chief cusps and 

 three or four small ones. There are four musculi papillares in the right ventricle, all of which 

 spring from the septal wall. They diminish in size from before backward, the anterior ones being 

 long and cylindrical. Their bases are connected with the lateral wall by trabecule camese. Usu- 



