The development of the human body; a manual of human embryology . -tinuous with the left lip of thefold which guards the openingof the sinus venosus and withthis forms the annulus of Vieus-sens of the adult heart. When the absorption of thesinus venosus into the wall ofthe right auricle has proceededso far that the veins communi-cate directly with the auricle,the vena cava superior opensinto it at the upper part of thedorsal wall, the vena cava in-ferior more laterally, and belowthis is the smaller opening ofthe coronary sinus. The upperportion of the right lip of thefold which originally surr
The development of the human body; a manual of human embryology . -tinuous with the left lip of thefold which guards the openingof the sinus venosus and withthis forms the annulus of Vieus-sens of the adult heart. When the absorption of thesinus venosus into the wall ofthe right auricle has proceededso far that the veins communi-cate directly with the auricle,the vena cava superior opensinto it at the upper part of thedorsal wall, the vena cava in-ferior more laterally, and belowthis is the smaller opening ofthe coronary sinus. The upperportion of the right lip of thefold which originally surroundedthe opening of the sinus venosus,together with the septum spu- rium, gradually disappears; the lower portion persists,however, and forms (1) the Eustachian valve (Fig. 131, Ve),guarding the opening of the inferior cava and directingthe blood entering by it toward the foramen ovale, and (2)the Thebesian valve, which guards the opening of the coro-nary sinus. At first no veins communicate with the leftauricle, but on the development of the lungs and the es-. Fig. 131.—Heart of Em-bryo op CM. FROMwhich Half of the RightAuricle Has Been Re-moved. jo, Foramen ovale; pa, pul-monary artery; Slt septumprimum; S2, septum secun-dum; Sa, systemic aorta;V, right ventricle; vci,and vcs, inferior and supe-rior venae cavse; Ve, Eus-tachian valve. 254. THE DEVELOPMENT OF THE HUMAN BODY. tablishment of their vessels, the pulmonary veins makeconnection with it. Two veins arise from each lung, andas they pass toward the heart they unite in pairs, the twovessels so formed again uniting to form a single short trunkwhich opens into the upper part of the auricle (Fig. 132,Vep)-. As is the case with the right auricle and thesinus venosus, the expansion of the left auricle bringsabout the absorption of the short single trunk into itswalls, and, the expansion continuing, the two vessels arealso absorbed, so that eventually the four primary veinsopen independently into the auricle. While the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
