616 DEVELOPMENT [cHAP.XLiil. 



the great majority of placentae which are subjected to examination, 

 although in some it is much more advanced than it is in others. 

 It occurs first in those tufts situated at the circumference of the 

 placenta, in which part the functions of the organ cease first. In 

 numerous instances, also, small masses of earthy phosphates are 

 found in the foetal tufts. Although fatty degeneration is doubtless 

 to be regarded, in many instances, as a morbid alteration, we must 

 at the same time bear in mind, that it does occur as a normal pro- 

 cess, and is one of the changes which ensues in tissues prior to 

 their absorption, after the period of their functional activity is 

 brought to a close. It seems to be one of the first of a series of 

 changes which ends in the removal of the tissue, or in the complete 

 disappearance of its ordinary characters. 



From what we have already said with reference to the structure 

 of the human decidua and placenta, it follows, that both are sepa- 

 rated at birth, and must be renewed at each successive pregnancy. 

 Both the uterine and foetal portions of the placenta are removed, 

 and of course a considerable lesion takes place at the time. The 

 great uterine veins are torn across, and the violent contraction of 

 the uterus alone prevents the death of the mother from haemor- 

 rhage at each period of parturition. Should the uterus, from any 

 cause, fail to contract, the death of the mother from haemorrhage 

 is inevitable, as the experience of almost every practitioner but too 

 clearly proves. Such a result, however, would not happen in the 

 ruminants, and in some other animals, where the foetal tufts are 

 readily withdrawn from the maternal sheaths, which merely con- 

 tract after parturition, and become much smaller, but suffer no 

 lesion whatever. 



Amnion. The early stages of the development of the amnion 

 have been already fully described (page 584) . It is formed upon 

 the same plan in all classes of animals', as it is in the human sub- 

 ject, as the later researches of Bischoff have conclusively shown. 

 The human ovum, at an early period of development, is seen to 

 be closely invested with the amnion ; which membrane, originally 

 consisting of two layers, is separated from the chorion by a con- 

 siderable space, which is entirely occupied by an albuminous ma- 

 terial of a jelly-like consistence, the " corps reticule " of Velpeau. 

 This substance is separated from the chorion by a thin membrane, 

 the endochorion ; so that it appears to be contained within a 

 special sac. 



The amnion consists of a closed sac, and it is prolonged over th< 



