CHAPTEE XIII. 





DISCHARGE OF THE FCETUS AND PLACENTA. 

 REGENERATION OF THE UTERINE TISSUES. 



DURING the growth of the embryo and its membranes, and the 

 development of the uterine mucous membrane into the decidua and 

 placenta, the muscular tissue of the uterus also increases in thickness, 

 while the whole organ enlarges, to accommodate the greater volume of 

 its contents. This increase of substance, which is mainly due to an un- 

 usual growth in the muscular walls of the organ, gives it a sufficient 

 degree of contractile power for the expulsion of the foatus at the time 

 of delivery. 



The enlargement of the amniotic cavity, and the increased quantity 

 of the amniotic fluid, also provide the requisite space and freedom for 

 the intra-uterine movements of the foetus. These movements begin to 

 be perceptible about the fifth month, at which time the development of 

 the muscular system has become sufficient to allow it a certain amount 

 of functional activity. During the latter months of pregnancy they 

 become more frequent and vigorous, and may often be felt by the hand 

 of the observer applied to the abdomen over the region of the uterus. 



The attachment of the embryo to the investing membranes of the egg 

 is at first by a very short and comparatively wide funnel-shaped con- 

 nection, consisting of the com- 

 mencement of the chorion, a part 

 of the amnion, and an abundant 

 deposit of gelatinous material 

 between the two, containing the 

 stem of the umbilical vesicle. 

 Subsequently, as the amniotic 

 cavity enlarges, the body of the 

 embiyo recedes farther from the 

 inner surface of the chorion, by 

 the elongation of its connecting 

 part ; and this part consequently 

 begins to present the appearance 

 of a cord (Fig, 275). It is still 

 surrounded with a thick layer of 

 gelatinous matter, by which it is 

 separated from its amniotic in- 

 vestment. As it emerges from 



the abdomen of the embryo at a" point where the abdominal walls will 

 afterward close round it, to form the umbilicus, it is known by the 



(763) 



Fig. 275. 



HUMAN EMBRYO AND ITS MEM- 

 BRANES, in the early period of gestation; 

 showing the commencement of formation of 

 the umbilical cord. 



