IMBEDDING OF OVUM 



65 



DEVELOPMENT OF THE FCETAL MEMBRANES AND PLACENTA; 

 IMBEDDING OF THE OVUM. 



Having determined the manner in which the principal organs of the body 

 make their appearance, we must now study in somewhat greater detail than 

 we have yet done the history of the chorion and amnion, in order to ascertain 

 how the placenta, or organ which nourishes the foetus, and the membranes which 

 protect it during its sojourn in the uterus, are developed. It will be necessary, 

 however, first to describe how the ovum is imbedded in the uterine mucous 

 membrane, and the changes that take place in that membrane during pregnancy. 



': 



FIG. 93. SECTION THROUGH AN OVUM OF THE FIRST WEEK. 

 (Reduced from Peters ; from Hertwig's Handbuch.) 



The section passes through the embryonic rudiment. Th, thrombus closing an opening on the surface 

 of the uterine epithelium, U.E. ; D, decidua. The very irregular strands of trophoblast are distinguished 

 by their darker tint. 



Imbedding of the ovum. The earliest known human ova are already 

 completely imbedded in the uterine mucous membrane. The site of implantation 

 in man is normally the posterior wall of the uterus near the fundus. 

 Peters' and Leopold's ova lay in this position ; their situation was not marked 

 by any projection of the mucous membrane beyond the general level of the 

 swollen surface. The blastocyst in Peters' case (fig. 93) was oval in shape. 

 The wall was relatively thick and already intimately related to the mucous mem- 

 brane (decidua). Over the ovum there was an area, one millimetre in diameter, 

 where the uterine epithelium was absent, and here there was a soft thrombus (Th), 

 which had a narrow stalk occupying the hole in the epithelium, and a broad head 

 spreading out like a mushroom over the edges of the opening. The uterine glands 

 in the neighbourhood of the blastocyst took a somewhat concentric course round 

 VOL. i. F 



