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In a Torpedo 12.8 mm long, the cardiac vessel has a smooth 

 lining, like other blood vessels (Fig. 10 A). Associated with it, there 

 are neither coronary arteries nor veins. At 16.5 mm scattered ele- 

 vations project into the auricular cavity, and an intercrescence between 



Fig. 10. Cross sections of the heart. A. Torpedo, 12.8 mm, H. E. C. 688, Sect. 243, 

 X 50 diams. B. Torpedo, 19.2 mm, H. E. C. 682, Sect. 387, X 50 diams. C. Torpedo, 

 37.0 mm, H. E. C. 757, Sect. 507, X 27 diams. D. Eabbit, 17.6 mm, 16V., days, H. E. C. 

 574, Sect. 506, X 27 diams. A. c. Coronary artery. Au. Auricle. .S'. V. Sinus venosus. 

 F. Ventricle. V. c. Coronary vein. V. C. I. Vena cava inferior. 



endothelium and myocardium has begun in the ventricle. There are 

 no coronary arteries. A vein has grown out from the venous sinus 

 into the adjacent connective tissue, and sends a branch of large calibre 

 on either side of the descending ventricular limb of the heart. These 



