ON THE DEVELOPMENT OF THE ATRIAL SEPTUM 

 AND THE VALVULAR APPARATUS IN THE RIGHT 

 ATRIUM OF THE PIG EMBRYO, WITH A NOTE ON 

 THE FENESTRATION OF THE ANTERIOR CAR- 

 DINAL VEINS 



C. V. MORRILL 



Department of Anatomy, Cornell University Medical College, New York City 



NINE FIGURES 



The method of formation of the atrial septum and nearly re- 

 lated parts in the mammalian heart has been known since the 

 careful investigations of Rose ('88 and '89), Born ('89), and 

 more recently Favaro ('13). These writers are in substantial 

 agreement regarding the structures concerned in this process, 

 though differing in some respect as to detail. The now classi- 

 cal work of Born on the rabbit has been used extensively as a 

 basis for descriptions of cardiac development in some of the 

 more recent text-books of embryology, notably by Hoch- 

 stetter ('01-'03) and Tandler ('12 and '13). Born in his ac- 

 count, which included some observations on human embryos, 

 corrected the error of His ('85) regarding the formation of the 

 atrial septum and its relation to the foramen ovale. His de- 

 scription differed from the earher one of Rose ('88) in several 

 important respects but later Rose ('89) accepted Born's correc- 

 tions. Rose and Favaro extended their observations to a num- 

 ber of different mammals, but not, as far as I am aware, to the 

 pig. Retzer ('08) published a brief note on the development of 

 the heart in which he claimed that Born's account of the atrial 

 septum in the rabbit could not be applied to the pig. Since pig 

 embryos are extensively used for study in American laboratories, 

 it seemed advisable to re-examine the development of the septal 



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