FUSION OF CARDIAC ANLAGES IN THE CAT 47- 



fusion of the mantles is complete (fig. 4) ; at 14 the formation of 

 the loop is initiated (fig. 7); and at 16 it is completed. The 

 fusion of the endothelial tubes begins in the embryo of 12 som- 

 ites, in that of 14 it is all but complete, and the embryo of 20 

 somites is the oldest that shows a remnant of septum between 

 the endothelial tubes (figs. 11, 13, and 16). 



THE MYOEPICARDIAL MANTLES 



There are many brief statements and illustrations of the myo- 

 epicardial mantles in the literature recording conditions in these 

 structures immediately antecedent to and during fusion, from 

 which nevertheless it would be impossible to compile a history 

 of the process. The observations of Kolliker, His, Tiirstig, 

 Schultze, Spee, Bonnet, Fleischmann, Selenka and Heape, are 

 as familiar as they are important and have been adequately 

 summarized by Mollier,i who has also included the less well 

 known and less accessible work of Martin, ^ which is valuable 

 for its excellent illustrations. Strahl and Carius^ and Parker," 

 alone have given continuous and detailed accounts of the pro- 

 cesses here considered. The former have illustrated by a series 

 of diagrammatic cross sections two different types of fusion, one 

 in which the formation of the ventral mesocardium antecedes 

 that of the dorsal, the other in which the converse obtains. 

 Two factors here come into play, first the width of the foregut 

 and second the primitive position of the bilateral cardiac an- 

 lages. The area of visceral mesoderm which intervenes be- 

 tween the myoepicardial mantle and the mesal angle of the pari- 

 etal cavity, they designate the retrocardiac plate, similarly that 

 between the mantle and the lateral angle the precardiac plate 



' MoUier, 8. Die crste AnLige ties Herzen bei den Wirbeltieren in Hertwig's 

 Haudbuch der vergl. und experiment. Entwickel. der Wirbeltiere, Jena, 1906, 

 Bd. 1, which see for literature. 



2 Martin. Lehrbuch der Anatomie der Hausteire. Bd. 1, Stuttgart, 1902. 



* Strahl and Carius. Beitrage zur Entwickelungsgeschichte des Herzens und 

 der Korperhohlen. Arch. f. Anat. und Physiol., Bd. 15, 1899. 



* Parker, Katherine M. The early development of the heart and anterior 

 vessels in Marsupials, with special reference to Perameles. Proc. Zool. Soc, 

 London, 1915, Pt. III. 



