The development of the human body; a manual of human embryology . ly-stalk; and,finally (p. 297), that the cloaca becomes divided into adorsal portion, which forms the lower part of the rectum,and a ventral portion, which is continuous with the allan-tois and receives the urinogenital ducts (Fig. 206). It isthe history of this ventral portion of the cloaca which isnow to be considered. It may be regarded as consisting of two portions, ananterior and a posterior, the line of insertion of the urino-genital ducts marking the junction of the two. The ante-rior or upper portion is destined to give
The development of the human body; a manual of human embryology . ly-stalk; and,finally (p. 297), that the cloaca becomes divided into adorsal portion, which forms the lower part of the rectum,and a ventral portion, which is continuous with the allan-tois and receives the urinogenital ducts (Fig. 206). It isthe history of this ventral portion of the cloaca which isnow to be considered. It may be regarded as consisting of two portions, ananterior and a posterior, the line of insertion of the urino-genital ducts marking the junction of the two. The ante-rior or upper portion is destined to give rise to the urinary 382 THE DEVELOPMENT OF THE HUMAN BODY. bladder (Fig. 206, b), while the lower one forms what isknown for a time as the urogenital sinus (sg). The bladder,when first differentiated, is a tubular structure, whose lu-men is continuous with that of the allantois, but after thesecond month it enlarges to become more sac-like, whilethe intra-embryonic portion of the allantois degenerates toa solid cord extending from the apex of the bladder to the. Fig. 206.—Reconstruction of the Cloacal Region of an Embryo of 14 MM. al, Allantois; 6, bladder; gt, genital tubercle; i, intestine; n, spinal cord;nc, notochord; r, rectum; sg, urinogenital sinus; ur, ureter; w, Wolf-fian duct.—(Keibel.) umbilicus and is known as the urachus. During the en-largement of the bladder the terminal portions of theurinogenital ducts become taken up into its walls, a pro-cess which continues until finally the ureters and Wolffianducts open into it separately, the ureters opening to thesides of and a little anterior to the ducts. This conditionis reached in embryos of about 14 mm. (Fig. 206), and in THE URETHRA. 3S50J later stages the interval between the two pairs of ductsis increased (Fig. 207), resulting in the formation of a shortcanal connecting the lower end of the bladder which re-ceives the ureters with the upper end of the urogenitalsinus, into which the Wolffian and Miillerian du
Size: 1782px × 1402px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
