58 THE STRUCTURE OF THE HUMAN PLACENTA. 



Dr. Sharpey has not described this inter-follicular substance, 

 as his attention appears to have been chiefly directed to the 

 follicles. As, however, it is to this iiiter-follicular substance, as 

 much as to the enlargement of the follicles themselves, that the 

 mucous membrane owes its increased thickness, it appears to me 

 worthy of being recorded. 



A uterus in the condition which has just been described, is 

 said to be lined with the decidua, consisting, as has been stated, of 

 an inter-follicular cellular substance, and of an extended network 

 of capillary blood-vessels. 



About the time at which the ovum reaches the uterus, the de- 

 veloped mucous membrane or decidua begins to secrete, the os 

 uteri becomes plugged up by this secretion, w r here it assumes the 

 form of elongated epithelial cells ; the cavity of the uterus becomes 

 filled with a fluid secretion, the " hydroperione" of Breschet, and 

 in the immediate neighbourhood of the ovum, the secretion con- 

 sists of cells of a spherical form. The cells which are separated 

 in the neighbourhood of the ovum I consider as a secretion of the 

 third order. They have passed off from the uterine glands entire, 

 and possess a power peculiar to the third order of secretions, the 

 power of undergoing further developement after being detached 

 from the germinal spots or membrane of the secreting organ. 



From what has now been stated, it appears, that the decidua 

 consists of tw r o distinct elements : the mucous membrane of the 

 uterus thickened by a peculiar developement, and of a non-vas- 

 cular cellular substance, the product of the uterine follicles. The 

 former constitutes at a later period the greater part of the de- 

 cidua vera, the latter, the decidua reflexa. This view of the 

 constitution of the decidua, clears up the doubts which were en- 

 tertained regarding the arrangement of these membranes at the 

 os uteri and entrances of the fallopian tubes. It is evident that 

 these orifices will be open or closed, just as the cellular secretion 

 is more or less plentiful, or in a state of more or less vigorous 

 developement. It also removes the difficulty of explaining how 

 the decidua covers the ovum, a difficulty which cannot be recon- 

 ciled with the views of Dr. Sharpey, who is obliged to suppose 

 the deposition of lymph, which is only the old view of the con- 

 stitution of the decidua. 



