FORMATION OP THE PLACENTA. 907 



756. The Maternal blood is conveyed into the Placental cavity by the 

 "curling arteries" of the uterus (Fig. 322, c, a, Fig. 323 d); and is received 

 back from it into the large veins that are commonly designated as sinuses 

 (Figs. 323, 324,6,6). "The utero-placental sinus system of veins is so 

 related to the placenta as to communicate with the interior of the cotyle- 

 dons, either at the outer edge of the placenta, where the so-called circular 

 sinus lies, or where the sinuses lie within the intercotyledouary decidual 

 dissepiments, or where they come into contact with the uterine face of the 

 placenta, close to the plane of entrance of the primary decidual dissepi- 

 ments into its substance. The communication is not as if the sinuses termi- 

 nated abruptly by open mouths, as has usually been described, but rather 

 by possessing cribriform apertures in their walls as they lie in contact with 

 the placenta. From the relation of the sinuses to the margins of the coty- 

 ledons, whilst the curling arteries penetrate their uterine surface near their 

 centre, the stream of maternal blood passes through each cotyledon from its 

 fcentre to its circumference, and is effectually brought into contact with the 

 whole of the foetal villi." The foetal vessels (Fig. 322, e, e; Fig. 323, c, c) 

 being bathed in this blood, as the branchiae of aquatic animals are in the 

 water that surrounds them, not only enable the foetal blood to exchange its 

 venous character for the arterial, by parting with its carbonic acid to the 

 maternal blood, and receiving oxygen from it ; but they also serve as root- 

 lets, by which certain nutritious elements of the maternal blood (probably 

 those composing the liquor sanguinis) are taken into the system of the foetus. 

 In this, they closely correspond with the villi of the intestinal canal ; and 

 there is this further very striking analogy, that the nutrient material is 

 selected and prepared by two sets of cells, one of which (the maternal) trans- 

 mits it to the other (the foetal), in the same manner as the epithelial cells of 

 the intestinal villi seem to take' up and prepare the nutrient matter, which 

 is destined to be still further assimilated by the cells that float in the circu- 

 lating current. It is probable, too, that the Placenta is to be regarded as 

 an excreting organ; serving for the removal, through the maternal blood, of 

 excrementitious matter whose continued circulation through the blood of the 

 foetus would be prejudicial to the latter. And it will be in this mode that 

 the blood of the mother may become impregnated with substances, or im- 

 pressed with attributes, originally belonging to the male parent; so as to 

 impart these to the products of subsequent conceptions by a different father 

 ( 769). l There is no more direct communication between the mother and 

 foetus than that which is afforded by this immersion of the foetal tufts in the 

 maternal blood; all the observations which have been supposed to prove the 

 existence of real vascular continuity, having been falsified by the extravasa- 

 tion of fluid, probably consequent upon the force used in injecting the ves- 

 sels. Moreover, the different size of the blood-corpuscles in the foetus and 

 in the parent shows the non-existence of any such communication. 



757. The formation of the Placenta, in the manner just described, com- 

 mences in the latter part of the second mouth ; during the third, the organ 

 acquires its proper character; and it subsequently goes on increasing, in ac- 

 cordance with the growth of the Ovum. Towards the end of the term of 

 gestation, however, it becomes more dense and less vascular; owing, it would 

 seem, to the obliteration of several of the minuter vessels, which are con- 

 verted into hard fibrous filaments. The vessels of the Uterus undergo great 

 enlargement throughout, but especially at the part to which the placenta is 



1 See, for various proofs that the mother may be poisoned through the presence of 

 noxious substances in the blood of the foetus, the Essay by Mr. Savory, entitled An 

 Experimental Inquiry into the Effect upon the Mother of Poisoning the Fcetus, Lon- 

 don, 1858. 



