Paramesonephric Duct

Degenerating mesonephric tubule ing Urogenital tubule mesentery

Ductuli efferer

Degenerating medullary cords

Mesonephric Surface epithelium duct

Mesonephric Surface epithelium duct ing Urogenital tubule mesentery

Ductuli efferer

Degenerating medullary cords

Cortical cords

Cortical cords

Female Cortical Cords

Figure 14.22 A. Transverse section of the ovary at the seventh week, showing degeneration of the primitive (medullary) sex cords and formation of the cortical cords. B. Ovary and genital ducts in the fifth month. Note degeneration of the medullary cords. The excretory mesonephric tubules (efferent ductules) do not communicate with the rete. The cortical zone ofthe ovary contains groups of oogonia surrounded by follicular cells.

close to the surface (Fig. 14.22 A). In the fourth month, these cords split into isolated cell clusters, with each surrounding one or more primitive germ cells (Fig. 14.22B). Germ cells subsequently develop into oogonia, and the surrounding epithelial cells, descendants ofthe surface epithelium, form follicular cells (see Chapter 1).

It may thus be stated that the genetic sex of an embryo is determined at the time of fertilization, depending on whether the spermatocyte carries an X or a Y chromosome. In embryos with an XX sex chromosome configuration, medullary cords of the gonad regress, and a secondary generation of cortical cords develops (Figs. 14.21 and 14.22). In embryos with anXY sex chromosome complex, medullary cords develop into testis cords, and secondary cortical cords fail to develop (Figs. 14.20 and 14.21).

GENITAL DUCTS Indifferent Stage

Initially both male and female embryos have two pairs of genital ducts: mesonephric (wolffian) ducts and paramesonephric (mullerian) ducts. The paramesonephric duct arises as a longitudinal invagination of the epithelium on the anterolateral surface of the urogenital ridge (Fig. 14.23). Cranially the duct opens into the abdominal cavity with a funnel-like structure. Caudally it first runs lateral to the mesonephric duct, then crosses it ventrally to grow caudomedially (Fig.14.23). In the midline it comes in close contact with the paramesonephric duct from the opposite side. The two ducts are initially

Ovaries Duct Paramesonephros
Figure 14.23 Genital ducts in the sixth week in the male (A) and female (B). The mesonephric and paramesonephric ducts are present in both. Note the excretory tubules of the mesonephros and their relation to the developing gonad in both sexes.

Abdominal ostium of uterine tube

Abdominal ostium of uterine tube

Fimbriae

Paramesonephric Mesonephric Pictures

Mesonephric duct

Suspensory ligament of ovary

Ligament of ovary proper

Fimbriae

Epoophoron Cortical cords of ovary

Mesonephric duct

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