200 



THE BLOOD VASCULAR SYSTEM 



It consists of a dense meshwork of cardiac muscle fibers rich in sarco- 

 plasm, in the form of a band taking origin in scattered fibrils in the 

 posterior wall of the right atrium near the septum in the atriovcutricular 

 groove (sinus region; hence, sinoventricular conducting system, Retzer, 

 1908), and coursing forward in the interatrial septum into the upper 

 anterior portion of the interventricular septum, where it divides into two 

 limbs which branch profusely and spread out in a complicated system 



of terminal branches, the 

 subendocardial Purkinje 

 fibers. Macroscopic-ally 

 the bundle has a grayish 

 appearance ; where it 

 passes from the intera- 

 trial to the interventricu- 

 lar septum (pars mem- 

 branacea septi) it ex- 

 pands into the so-called 

 node. In man the right 

 limb is much smaller 

 than the left. 



The bundle of the 

 calf's heart has been re- 

 constructed by De Witt 

 (Anat. Rec., 3, 9, 1909). 

 Curran (Anat. Eec., 3, 

 12, 1909) has described 

 a constant bursa or lubri- 

 (De Witt, Anat. Rec., 3, 9, 1909.) eating mechanism in re- 



lation with the bundle, 



furnishing protection against friction during contraction of the heart. 

 He describes "its connection with all parts of both auricles through three 

 large trunks and a number of smaller twigs, and not, as was once 

 thought, merely arising in the right auricle only." 



Tawara (1906) first carefully described the histology of this bun- 

 dle in several mammals, including man. De Witt more recently (1909) 

 has extended the study in this same field. "In the sheep and calf, where 

 the fibers are most typical and most clearly differentiated from the 

 myocardial fibers, the fibers are much larger than the myocardial fibers, 

 with fewer fibrils and much more sarcoplasm." She describes the bundle 

 as a muscular syncytium. "Connective tissue and especially elastic fibers 



FIG. 216. RECONSTRUCTION OP THE SINOVEN- 

 TRICULAR .SYSTEM (BUNDLE OF His) OF THE 

 CALF'S HEART. 



