THE HEART 



37 



The Sinus Venosus in the Human Heart. The sinus venosus 

 is of importance in primitive vertebrate hearts, because it is here 

 that many authorities have observed the origin of the heart rhythm 

 (Gaskell, Mac William, Engelmann). This fact makes it essential 

 for us to know what parts represent the sinus venosus in the 



FIG. 1. A generalised type of vertebrate heart-*-co'nibining features found in 

 the eel, dogfish, and frog (Keith) ; a, sinus venosus and veins ; b, auricular canal ; 

 c, auricle ; d, ventricle ; e, bulbus cordis ; /, aorta ; 1-1, sino-auricular junction 

 and venous valves ; 2-2, canalo-auricular junction ; 3-3, annular jart of auricle ; 

 4-4, invaginated jtart of auricle ; 5, bulbo-ventricular junction. 



mammalian heart, since in them one might expect the heart 

 rhythm to arise. 



The sinus venosus is represented in the mammalian heart by 

 four remnants: (1) The termination of the superior vena cava 

 (the right duct of Cuvier). (2) The coronary sinus (the left duct 

 of Cuvier). (3) A stratum submerged beneath auricular tissue at 

 the taenia terminalis. (4) The remnants of the venous valves, 

 i.e. the Thebesian and Eustachian valves. 



This does not represent a large amount of tissue, and it is diffi- 

 cult to trace in the mammalian heart. I would, however, draw 

 attention to the occurrence in all mammalian hearts examined 

 of a remarkable remnant of primitive fibres persisting at the sino- 



