CHANGES IN THE UTERUS. 



51 



imbedded in the muscular coat of the uterus, and retain their epithelium. After 

 separation of the placenta from the uterine wall at parturition, the uterine mucous 

 membrane, with its epithelium and glands, becomes renewed from this deepest portion 

 of the decidua serotina. 



The most important changes of structure occur in the superficial part of the 

 placental decidua, after the disappearance of the glands. The exact manner in 

 which these changes take place has not been followed out, but the ultimate result is 

 the replacement of the whole of this portion of the decidua, with the exception of a 



Fig. 54. SECTIONS ILLUSTRATING THE STRUCTURE OF THE PLACENTA (Minot). 



A, vertical section through the margin of a placenta at full term ; D, J), deep layer of decidua ; 

 Vi, chorionic villi variously cut, their bloodvessels injected ; Si, marginal space of the placenta, 

 nearly free from villi ; r/, aborted villi beyond the placenta ; Fib, canalized fibrine of Laughans, 

 produced, according to Minot, by transformation of the superficial layer of the chorionic epiblast. 



B, deeidual tissue from a placenta at full term ; v, a bloodvessel ; d, d', decidual cells ; the latter 

 with several nuclei. 



comparatively narrow basal layer next to the spongy structure, into a series of inter- 

 communicating vascular sinuses, which together constitute an immense flattened 

 space (intervillous space), bounded internally (toward the uterine wall) by the basal 

 layer just referred to, and externally by the chorion ; also, * according to some 

 authors, by a thin layer of decidua, the sulchorionic membrane of Turner, which is 

 described as lying immediately under the chorion of the ovum but so intimately 

 incorporated with it as to be with difficulty demonstrable as a separate stratum 

 except at the edge of the placenta. 



From the basal layer, partitions of fibrous decidual tissue pass towards the 

 chorionic surface, and serve to partially sub-divide the labyrinth of vascular space? or 

 sinuses into a number of loculi (cotyledons). Each of these loculi is occupied by an 



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