SEPARATION OF THE DECIDUA AT BIRTH. 



as to produce a partial blockage of these veins, preparatory to the detachment of the 

 placenta from the layer. 



The villi do not at first cover the whole surface of the ovum, but are deficient at 

 the embryonic, and perhaps also at the opposite, pole. In the earliest human ovum 

 which has hitherto been described, 

 that of Eeichert (fig. 58), the villi, 

 which are quite simple, occur in a 

 broad zone around the circumference 

 of the ovum, leaving the (somewhat 

 flattened) poles smooth and free 

 from villi, and on one of these poles 

 a thickening of the wall of the 

 vesicle could be detected, which was 

 probably the embryonic area. But 

 in all other early human ova which 

 have been noticed, the chorion, 

 which is now formed by the false 

 amnion, is covered with ramified 

 villi (shaggy chorion), and these are 

 already vascularized from the allan- 

 tois, and have grown into the sub- 

 stance of the decidua reflexa and the Fig . GO. -PORTION OF AN INJECTED VILLUS FROM A 

 decidua serotina, the formation of PLACENTA OP ABOUT FIVE MONTHS (Minot). 



the placenta having already begun. 



Separation of the decidua at birth, and regeneration cf the 

 uterine mucous membrane. In parturition, the pressure of the contracting 

 muscular walls upon the uterine contents, and especially upon the amniotic fluid, 

 causes a bulging of the membranes (consisting of the combined deciduse, the 

 chorion, and the amnion) through the os uteri. When the membranes are ruptured, 

 the amniotic fluid first escapes, and subsequently th& foetus is expelled. With 

 further contraction of the uterus, the placenta becomes detached from the uterine 

 wall, separating along the plane of the dilated parts of the glands (stratum spongio- 

 num of the decidua serotina), and as it is expelled, the separation extends around the 

 decidua lining the rest of the uterus, which appears in the " after-birth " along with 

 the chorion and amnion as a thin membranous skirt to the edge of the placenta. The 

 deepest part of the decidua containing the bases of the uterine glands is everywhere 

 left in connection with the muscular tissue, and from these basal portions of the 

 glands, first the whole of the uterine glands, and subsequently the lining epithelium 

 of the uterus become gradually regenerated. 



BECENT LITERATURE. 



Allen, W., Ompkalo-mesenteric remains in mammals. Journ. Anat. and PhysioL, xvii., 1883. 



Beneden, Ed. van, De la fixation du Uastocyste a la muqueuse uterine chez le murin (Vesper- 

 tilio murinus}. Bullet, tie 1'Acad. roy. de Belgiqne, Ser. iii., T. xv. ; De la formation et de la constitu- 

 tion du placenta chc~ le murin (Vcspertilio murinus}. Bulletins de 1'Acad. roy. de Belgique, T. xv., 

 1888. 



Beneden, E. v., et Julin, Reclicrchcs sur la formation des annexes fcetales chezles mammiferes. 

 Arch, de biologic, v. 1884. 



Bonnet, B., Die Utcrinmilch und Hire Bedeutunn fur die Frucht. Beitra^s zur Biologic, 1882 ; 

 Die Eihdute de* Pferdes. Verhandl. d. anat* Gesellschaft, 1889. 



Bumm, Zur Kenntniss der Uteroplacentaryefiisse. Archiv f. Gynakologie, xxxv., xxxvii. j Zur 

 Anat. d. Placenta. Wiirzburg Sitzungsb., 1889. 



Cadiat, L'allantoide. Gaz. med. de Paris, 4 seY. vi., 1887. 



Caldwell, W. H., On the arrangement of the embryonic membranes in marsupial animalsi 

 Quarterly Journal of Microsc. Science, xxiv., 1884. 



Colucci, Gr., Di alcuni novi dati di struttura delhi placenta unianrt) 1887. 



