REPRODUCTION 



193 



luteum which secretes several hormones that prepare the uterus, 

 both structurally and physiologically, for the reception of the egg 

 and the attachment of the embryo. Moreover, certain hormones 

 secreted by the ovary during pregnancy directly influence the 

 pituitary gland which in turn induces the development and func- 



«/__ 



Fig. 134A. — Diagrammatic section of the human uterus with developing 

 embryo. The embryo (/<) is suspended in a fluid-filled cavity (c) surrounded 

 by embryonic membranes (e) and by tissue (/) from the uterus itself. The sole 

 path of communication between embryo and mother is by blood in vessels 

 passing up through the umbilical cord (i), spreading out into capillaries in the 

 placenta (6) and there coming into close relations with the maternal blood 

 supply. The openings of the oviducts (d) into the uterus become closed during 

 the development of the embryo, a, dorsal wall of uterus; 6, placenta; c, fluid- 

 filled cavity of amnion; d, openings of oviducts (Fallopian tubes); e, embryonic 

 membranes; /, uterine tissue; g, uterine cavity; h, embryo; i, umbilical cord. 



tioning of the mammary glands. At least two hormones are in- 

 volved; one directly stimulates the development of the mammary 

 glands, while another prevents their functioning until it is inacti- 

 vated at the birth of the offspring. 



3. The Urogenital System 



We must now outline the structural interrelations of the urinary 

 and reproductive organs forming the urogenital system. It has 



