The development of the human body; a manual of human embryology . ke place It is possible,therefore, to recognize two por-tions in the embryonic coelom, ananterior one, the parietal cavity(His), which is never connectedlaterally with the extra-embry-onic cavity, and a posterior one,the trunk cavity, which is so con-nected. The heart is situated inthe parietal cavity, a consider-able portion of which is destinedto become the pericardial the parietal cavity liesimmediately anterior to the stillwide yolk-stalk, as may be seenfrom the position of the heart inthe embryo shown in Fig. 4
The development of the human body; a manual of human embryology . ke place It is possible,therefore, to recognize two por-tions in the embryonic coelom, ananterior one, the parietal cavity(His), which is never connectedlaterally with the extra-embry-onic cavity, and a posterior one,the trunk cavity, which is so con-nected. The heart is situated inthe parietal cavity, a consider-able portion of which is destinedto become the pericardial the parietal cavity liesimmediately anterior to the stillwide yolk-stalk, as may be seenfrom the position of the heart inthe embryo shown in Fig. 42, itis bounded posteriorly by theyolk-stalk. This boundary iscomplete, however, only in themedian line, the cavity beingcontinuous on either side of theyolk-stalk with the trunk-cavityby passages which have beentermed the recessus parietales(Fig. 179, Bp and Rca). Pass-ing forward toward the heart in the splanchnic mesoderm which surrounds the yolk-stalkare the large omphalo-mesenteric veins, one on eitherside, and these shortly become so large as to bring the. Rca Fig. 179.—Reconstructionof a Rabbit Embryo ofEight Days, with thePericardial Cavity LaidOpen. A, Auricle; Aob, aortic bulb;, auriculo-ventricularcommunication; Bp, ven-tral parietal recess; Om,omphalo - mesenteric vein ;Pc, pericardial cavity; Rca,dorsal parietal recess; sv,sinusvenosus; V, ventricle.—{His.) 336 THE DEVELOPMENT OF THE HUMAN BODY. splanchnic mesoderm in which they lie in contact withthe somatic mesoderm which forms the lateral wall ofeach recess. Fusion of the two layers of mesodermalong the course of the veins now takes place, andeach recess thus becomes divided into two parallel pas-sages, which have been termed the dorsal (Fig. 180, rpd)and ventral (rpv) parietal recesses. Later the two veinsfuse in the upper portion of their course to form the begin-ning of the sinus venosus, with the result that the ventralrecesses become closed below and their continuity with the
Size: 1118px × 2236px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
