PLACENTA. 383 



intra-placental circulation of maternal blood as definitively 

 established. 1 



Structure of the Fully-developed Placenta. The placenta 

 of the human subject presents certain differences in its struct- 

 ure at various periods of utero-gestation, most of which have 

 been indicated in treating of its development. At about the 

 end of the third month, the limits of the placenta become 

 distinct, and the organ rapidly assumes the anatomical char- 

 acters observed after it may be said to be fully developed. It 

 then occupies about one-third of the uterine mucous mem- 

 brane, and is generally rounded or ovoid in form, with a 

 distinct border connected with the decidua and the chorion. 

 It is from seven to nine inches in diameter, a little more than 

 an inch in thickness at the point of penetration of the um- 

 bilical cord, slightly attenuated toward the border, and weighs 

 from fifteen to thirty ounces. Its foetal surface is covered 

 with the smooth amniotic membrane, and its uterine surface, 

 when detached, is rough, and divided into numerous irregular 

 lobes or cotyledons, from half an inch to an inch and a half 

 in diameter. Between these lobes, are membranes, called 

 dissepiments, which penetrate into the substance of the organ, 

 frequently as far as the foetal surface. 2 



Upon the uterine surface, is a thin, soft membrane, some- 

 times called the decidua serotina. This is merely a portion of 

 the mucous membrane of the uterus situated next the muscu- 

 lar walls, the greater part of it not being thrown off with the 

 placenta. It is composed of amorphous matter, numerous 

 granulations, and colossal cells with enlarged and multiple 

 nuclei. If we scrape the uterine surface of a fresh placenta, 

 these cells appear, on microscopical observation, very much 



1 TURNER, Observations on the Structure of the Human Placenta. Journal of 

 Anatomy and Physiology, Cambridge and London, 1873, vol. vii., p. 133. 



LAURE, Le placenta. Revue scientifique, Paris, 1873-'74, tomes xii., xiii., 

 p. 786. 



2 FARRE, Cyclopaedia of Anatomy and Physiology, London, 1859, vol. v., 

 Supplement, p. 715, et seg. t Article, Uterus and its Appendages. 



155 



