906 



OF GENERATION ACTION OF THE FEMALE. 



placenta, which may be regarded in its adult state (as well pointed out by 

 Dr. J. Reid 1 ) in the light of a large sac formed by a prolongation of the 

 inner coat of the uterine vessels ; against the foetal surface of which sac the 

 tufts just described may be said to push themselves, so as to dip down into it, 

 carrying before them a portion of its thin wall, which constitutes a sheath to 

 each tuft. Now as every extension of the uterine vessels carries the decidua 

 before it, every one of the vascular tufts that dips down into it will be 

 covered with a layer of the cellular structure of the latter ; and the foetal 

 portion of each tuft will thus be generally inclosed in a layer of maternal 

 cells and basement-membrane (Fig. 322, a, b, c).' 2 The whole interior of the 



FIG. 323. 





Section of a portion of a fully-formed Placenta, with the part of the Uterus to which it is attached: 

 a, umbilical (ord ; 6, 6, section of uterus, showing the venous sinuses ; c, c, c, branches of the umbilical 

 vessels ; d, d, curling arteries of the uterus. 



Placental cavity soon becomes (Fig. 323) intersected by numerous tufts of 

 foetal vessels disposed in fringes, and bound down by reflexions of the deli- 

 cate membrane that forms its proper wall ; just as the intestines are held in 

 their places by the reflexions of the peritoneum that covers them. This 

 view was suggested to Dr. Reid by the very interesting fact, that the tufts 

 of fa'tal vessels not unfrequeutly extend beyond the uterine surface of the 

 placenta, and dip down into the uterine sinuses, where they are still covered 

 and held in their places by reflexions of the same membrane. All the 

 bands which connect and tie down the tufts are formed of the same elements 

 as the envelopes of the tufts themselves ; namely, a fold of the lining mem- 

 brane of the decidual sinuses, and a layer of the cellular decidua. 



that the decidua serotina does not form a complete and continuous membranous septum 

 between the uterus and placenta, but that its continuity is in various Idealities inter- 

 rupted to allow of the penetration of many nf the placental villi into the utero- 

 placental vessels, into which they project free and naked. 



1 Kilin. Med. and Surg. Journ., January, 1841 ; and Anat., Pliys., and Pathol. 

 Researches, chap. viii. 



2 See Turner, Observations on the Structure of the Human Placenta, in Humphry 

 and Turner's Journal of Anatomy and Physiology, vol. vii, 1873, p. 1'20, in which 

 the literature of the subject will be found. 



