FUSION OF CARDIAC ANLAGES IN THE CAT 05 



the anastomosis between the oniphalo-mesentei-ic veins. In it 

 are three angiocysts. Two are very small; the more caudal of 

 these is in process of annexation to the right ventricle, the other 

 is attached by its wall to the left ventricle but does not commun- 

 icate with its lumen. The largest angiocyst is elongated and 

 has important connections. It communicates cephalad with 

 the isthmian region of each bulbus and so establishes the first 



■'' ^ 



<^^ 



r 



i^ 



Fig. II Reconstruction of the luniina of the endothelial heart tubes and adja- 

 cent vessels of a cat embyro of twelve pairs of somites. Columbia Collection, 

 Xo. 547. X 300. Reduced one-half. ^ Median angiocyst; ^, bulb; 3, ventricle; 

 4, atrio-venous angle; 5, omphalo-mesenteric vein; 6, forming aortic arches. 



continuity of lumen between the endothelial tubes. In addi- 

 tion it has a small connection with the right ventricle. Thus 

 the median angiocysts play a role in the coalescence of the en- 

 dothelial anlages analogous to that of the middle plate in the 

 fusion of the myoepicardial mantles. For the rest the changes 

 accomplished in this stage are easily appreciated on comparison 

 with the heart of the embryo of 11 somites (fig. 10). The cardio- 



THE AMEKKAX JOrRNAI, OF ANATOMY, VOL. 20, NO 1 



