275 



branches, the right and left coronary veins, run along the auriculo- 

 ventricular groove. The somewhat older embryo, B'ig. 10 B, illustrates 

 the position of the veins and the formation of the sinusoids. 



The coronary arteries are first seen in embryos of 22 mm, and 

 are still small in those of 25. Arising from the efferent branchial 

 vessels they follow the posterior aortic trunks (which divide to supply 

 the 5th and 6th arches) back to the ventral aorta; thence they proceed, 

 one on either side, down to the bulbus arteriosus, in the tissue of 

 which they disappear. 



In the 37 mm Torpedo the coronary arteries and veins have united 

 by capillaries, which are abundant in the epicardial connective tissue 

 (Fig. IOC). The right and left coronary veins now leave the venous 

 sinus separately, as shown in the figure, and their number has been 

 increased by other smaller outgrowths. Sinusoids are absent from the 

 bulbus arteriosus and the venous sinus. In the auricles they are 

 marked out by a loose meshwork of slender trabeculae. Except in the 

 corners and extremities of the auricles they appear greatly distended. 

 In the ventricle they are typical and numerous, reaching almost to the 

 epicardium. 



In one place in this embryo, a connection between an epicardial 

 vein and a sinusoid can be seen distinctly. Though the two sets of 

 vessels are often close together, no anastomosis between them can be 

 found in the younger embryos. In the adult hearts of Amia') and 

 the Sunfish^), G. H. Parker has found that air blown gently through 

 the coronary veins bubbles out in the ventricular cavity. Prof. Parker 

 found also connections between the coronary system and the auricles. 

 These do not appear in the Torpedo embryos, which, at 51 mm, have 

 no cai)illaries in the auricular walls except along the auriculo-ventri- 

 cular groove. 



The adult heart of fishes remains supplied with sinusoids, but over 

 the ventricle an outer compact layer of muscle probably contains ca- 

 pillaries derived from the coronary vessels. Hyrtl, Gegenbaur, and 

 Martin ^) disagree as to the extent of the capillaries inward, a matter 



1) G. H. Parker and F. K. Davis, The blood vessels of the heart 

 in Carcharias, Raja, and Amia. Proc. of the Bost. Soc. of Nat. Hist., 

 Vol. 29, 1899, p. 173. 



2) G. H. Parker, Note on the blood vessels of the heart in the 

 Sunfish. Anat. Anz., Bd. 17, 1900, p. 315. 



3) H. Martin, Recherches sur les arteres coronaires du coeur, p. 16 

 and p. 31. Paris 1894 



18* 



