the fusion of the cardiac anlages and the 



for:\iation of the cardiac loop in 



the cat (felis domestica) 



\ 



H. VON W. SCHULTE 



FroDi Ihc Anatomical Laboratory of Cohonhia University 

 \ 



SIXTEEN FIGURES 



111 the trausfonnation of the bilateral anlages of the heart 

 into a single median organ, two processes are to be distinguished, 

 the fusion of the myoepicardial mantles and the fusion of the 

 endothelial tubes. For while the union of the mantles is a nec- 

 essary condition of the coalescence of the tubes and its char- 

 acter determines the general features of the endothehal fusion, 

 yet the latter process is relative^ much retarded and evinces a 

 considerable degree of independence in many details. For these 

 reasons it will be convenient to follow the two processes sepa- 

 rately. 



This study is based upon the now numerous earlj^ embryos 

 of the cat in the Columbia Embryological Collection. These 

 were cut in transverse serial sections of 13.3 fx and variously 

 stained. In selected embryos reconstructions by the Born 

 method were made of the myoepicardium, of the endothelium 

 and mesenchyme, and finally of the lumina of the heart tubes 

 and angiocysts. By a comparison of the last two it is possible 

 to ascertain the precise limits of the solid and hollow parts of 

 the anlages. 



The processes of approximation, of fusion, and of loop-forma- 

 tion take place in a short period of development as measured by 

 the rate of formation of the mesodermic somites, the whole 

 duration of these changes in the cat falling between the stages 

 8 and 21 somites. At 8 somites (fig. 1) ,the foregut in the car- 

 diac region is widely open and the splanchnopleure is spread out 



