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DISCHARGE OF THE OVUM, 



CHAPTER XIII. 



DISCHARGE OF THE OYUM, AND RETROGRADE 

 DEVELOPMENT (INVOLUTION) OF THE UTERUS. 



DURING the growth of the ovum and the formation of the pla- 

 cental structures, the muscular substance of the uterus also increases 

 in thickness, while the whole organ enlarges, in order to accommo- 

 date the growing foetus and its appendages. The relative positions 

 of the amnion and chorion, furthermore, undergo a change during 

 the latter periods of gestation, and the umbilical cord becomes 

 developed, at the same time, in the following manner. 



In the earlier periods of foetal life, the umbilical cord consists 

 simply of that portion of the allantois lying next the abdomen. It 

 is then very short, and contains the umbilical vessels running in a 

 nearly straight course, and parallel with each other, from the abdo- 

 men of the foetus to the external portions of the chorion. At this 

 time the amnion closely invests the body of the foetus, so that the 



size of its cavity is but little larger 

 than that of the foetus. (Fig. 229.) 

 The space between the amnion 

 and the chorion is then occupied 

 by an amorphous gelatinous ma- 

 terial, in which lies imbedded the 

 umbilical vesicle. 



Afterward, however, the am- 

 nion enlarges faster than the cho- 

 rion, and encroaches upon the 

 layer of gelatinous matter situated 

 between the two (Fig. 230), at 

 the same time that an albuminous 

 fluid, the " amniotic fluid," is ex- 

 uded into its cavity, in constantly 



increasing quantity. Subsequently, the gelatinous layer, above de- 

 scribed, altogether disappears, and the amnion, at about the begin- 



Fig. 229. 



HUMAN OVTTM about the end of the first 

 month. -1. Umbilical vesicle. 2. Amnion. 3. 

 Chorion. 



