152 



ELEMENTS OF MAMMALIAN ANATOMY 



of the ventricles. The walls of the atria are thin in comparison 

 with the walls of the left ventricle, which are twice as thick 

 as the walls of the right ventricle (Fig. 76). 



The walls of the heart are made up chiefly of a peculiar type of 

 striped muscle-cardiac muscle forming the myocardium. In 



1.^ 



Fig. 76. — Ventral Aspect of the 

 Heart with Its Caudal Third Cut 

 OFF Transversely. 



a. Adipose tissue; be, innominate 

 artery; la, left atrium; Iv, left ven- 

 tricle; Ic, left carotid artery; o, 

 ductus arteriosus; pv, pulmonary 

 vein; ha, pulmonary artery; pc, su- 

 perior vena cava; psc, inferior vena 

 cava; ra, right atrium; re, right 

 carotid artery; rs, right subclavian 

 artery; rv, right ventricle; sh, left 

 subclavian artery; Ir, trachea. 



Fig. 77. — Dorsal Aspect of the 

 Heart of the Cat. 

 ao. Aorta; ap, apex; as, azygos 

 vein; he, innominate artery; ea, 

 coronary artery; cv, coronary vein; I, 

 left atrium; Ic, left carotid artery; 

 Ish, left subclavian artery; p, inferior 

 vena cava; pc, superior vena cava; 

 pa, pulmonary artery dividing into 

 its right and left branches; ra, right 

 atrium; re, right carotid; rs, right 

 subclavian; v, pulmonary veins. 



addition to the cardiac muscle there are certain other fibers 

 known as Purkinji fibers which form a network just below the 

 endocardium. In 1893 W. His Jr. discovered a bundle of 

 muscle fibres arising in the posterior wall of the right atrium 

 which extends down into the ventricular septum and connects 

 the atrial and ventricular musculature. This has since been 

 known as the atrioventricular bundle of His. In 1906 Tawara 



