The development of the human body; a manual of human embryology . ty to theWolffian. This is known as the Miillerian duct (Fig. 200,Md). Its development is preceded by the appearance ofa distinct ridge or fold upon the ventral surface of theWolffian body, extending from the under surface of thediaphragm above to the urogenital sinus below and con-taining in the lower portion of its course the Wolffianduct (Fig. 197). Near the anterior end of the mesoneph-ros there grows into this fold an evagination from theperitoneum covering the Wolffian ridge and by the pro-liferation of the cells at its ti
The development of the human body; a manual of human embryology . ty to theWolffian. This is known as the Miillerian duct (Fig. 200,Md). Its development is preceded by the appearance ofa distinct ridge or fold upon the ventral surface of theWolffian body, extending from the under surface of thediaphragm above to the urogenital sinus below and con-taining in the lower portion of its course the Wolffianduct (Fig. 197). Near the anterior end of the mesoneph-ros there grows into this fold an evagination from theperitoneum covering the Wolffian ridge and by the pro-liferation of the cells at its tip this evagination graduallyextends downward in the substance of the ridge, and inembryos of 22 mm. has reached the urogenital sinus. Asthey approach the sinus, the right and left evaginationsor Miillerian ducts gradually approach one another andfinally fuse together to form a single tube in the lower partof their course, but they remain distinct above, each tuberetaining its original opening into the peritoneal 37° THE DEVELOPMENT OF THE HUMAN Fig. 200.—Transverse Section through the Abdominal Region ofan Embryo of 25 mm. Ao, Aorta; B, bladder; /, intestine; L, liver; M, muscle; Md, Miillerianduct; N, spinal cord; Ov, ovary; RA, rectus abdominis; Sg, spinalganglion; UA, umbilical artery; Ur, ureter; v, vertebra; W, Wolffianbody; Wd, Wolffian duct.—(Keibel.) THE GENITAL RIDGE. 371 The first indication of the appearance of the genitalridge is the assumption of a high columnar form by theepithelial cells of the upper part of the mesial surface ofthe Wolffian ridge, and shortly after this thickening of theepithelium has appeared a condensation of the underlyingmesenchyme occurs (Fig. 194). At first the ridge is ofinsignificant dimensions compared with the more vol-uminous Wolffian body, but as the degeneration of thelatter proceeds the relative size of the two structures be-comes reversed and the genital ridge forms a markedprominence attached to the surface
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
