. Cunningham's Text-book of anatomy. Anatomy. 38 HUMAN EMBBYOLOGY. The growth at the nodal point not only produces a head fold, but at the same time it forces the cephalic end of the primitive streak caudally over the caudal end of thf embryonic area, thus forming a tail fold. As the head, and tail folds of the embryo are produced by the longitudinal increase of the embryonic area, transverse growth of the area results in the forma- tion of right and left lateral folds (Figs. 37, 39), and as the various folds are formed the embryo rises like a mushroom into the interior of the amnion cavity. T
. Cunningham's Text-book of anatomy. Anatomy. 38 HUMAN EMBBYOLOGY. The growth at the nodal point not only produces a head fold, but at the same time it forces the cephalic end of the primitive streak caudally over the caudal end of thf embryonic area, thus forming a tail fold. As the head, and tail folds of the embryo are produced by the longitudinal increase of the embryonic area, transverse growth of the area results in the forma- tion of right and left lateral folds (Figs. 37, 39), and as the various folds are formed the embryo rises like a mushroom into the interior of the amnion cavity. The portion of the entodermal sac which is enclosed, within the hollow embryo, formed by the folding of the embryonic area, is the primitive entodermal alimentary canal. The part which remains outside the embryo is the yolk sac, and the passage of communication between the two is the vitello-intestinal duct. That portion of the primitive entodermal alimentary canal which lies in the head fold is termed the fore-gut, the part in the tail fold is the hind-gut, and the intermediate portion which is in free communication with the yolk-sac is the mid-gut. As the extension of the embryonic area and its folding proceed, the margin of the area which remains relatively stationary becomes the margin of an orifice, on Spinal part of neural tube Notochord Fore-gut Hind-brain Mid-gut Amnion cavity Ectoderm of amnion Mesoderm of amnion. Bucco- pharyngeal membrane Fore-brai Stoniatodseum" Pericardium (heart not shown) Cloacal membrane Body stalk Rudiment of liver Allantoic diverticulum Mesoderm of yolk-sac Entoderm Umbilical orifice Fig. 50.—Schema of Sagittal Section of Embryo after the Folding has defined both the Fore- gut AND HlND-GDT AREAS. the ventral aspect of the embryo, through which the primitive alimentary canal of the embryo and the intra-embryonic part of the ccelom communicate, respectively, with the yolk sac and the extra-embryonic portion of the ccelom. This orifice is t
Size: 1990px × 1256px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
