of Human Monstrosity. 235 



is higher in the scale, so does the addition of the accessory parts 

 of its ovum occur in situations more remote from the ovary. 



As the human ovum passes along the tube, the germinative 

 membrane is more and more developed : and the activity of the 

 uterus is at the same time exalted. This organ secretes from its 

 entire surface a soft matter, which is spongy, reticulated, filamen- 

 tous, about the tenth of an inch in thickness. The secretion is 

 called by Hunter the decidua. It represents, of course, the exact 

 shape of the uterus, of which it is a cast, and closes all the open- 

 ings into that organ. Its attachment to the uterus is in the early 

 stages very slight, being here and there connected to its walls by 

 a few very delicate blood vessels. It at first merely adheres to 

 the uterus, as a secretion, and afterwards becomes united to it by 

 vessels. The ovum passing from the tube which opens obliquely 

 into the uterus, meets the obstruction of the decidua : this, from 

 its slight adhesion to the walls of the uterus, it is able to detach 

 for a greater or less space, and then sinks, by its weight, into 

 the body of that viscus. Thus as the ovum descends to the more 

 central region of the uterus, it carries before it a duplicative of 

 the decidua which supports it and keeps it in a near connexion 

 with the uterus. The doubled portion is called the decidua re- 

 flexa. From this description it follows that at the place where 

 the decidua is reflected, the uterus is deprived of its covering. A 

 new secretion from the uterus shortly supplies the deficiency, and 

 this is the seat of the future placenta. The human ovum passes 

 into the uterus at the end of the second week after impregnation. 

 The reflection of the decidua begins at the end of the third. 

 The reflected portion receives a considerable supply of vessels 

 from the uterus, and soon becomes the thicker of the two. In 

 process of time however, from constant distension by the gradu- 



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