ZONULAU, DISCOIDAL, AND DIFFUSE PLACENTiE. 107 



down between the decidual lamellae. The slightest traction 

 exerted upon the cord causes the placenta to separate along the 

 line e, m, m, e, bringing with it, of course, the cup-shaped 

 deeidua, d* 



It is obvious, from the above description, that the " pedun- 

 culate and cotyloid '' placenta of the Rat does not " consist 

 of foetal parts exclusively," but that, on the contrary, as 

 Eschricht has so well pointed out, " the organic interblending 

 of the circulatory organs of mother and offspring " is as com- 

 plete in the Rat as in Man ; and that, therefore, the concluding 

 paragraph of the citation from Professor Owen's paper ought to 

 be reversed. 



The Camivora develop a well-marked deeidua, and their 



* My friend Professor Eolleston has made the following statements in a paper 

 which will shortly appear iu the Zoological Society's Transactions. 



1. The Rat's afterbirth consists of a saucer-shaped deciduous serotina, and a 

 button shaped placenta proper. Afterbirths made up of these two elements may 

 be found in the stomachs of animals of this species after parturition, as they, like 

 many other Mammals below the Simiadm, devour them. Under these circum- 

 stances, the two constituent factors of the afterbirth may either be found in their 

 normal connection, or they may be separated one from the other. 



2. The non-deciduous part of the serotina forms in the Rat, after parturition, a 

 hernial protrusion into the mesometrium, which has been mistaken for a developing 

 ovum (see Hunterian Catalogue, Phys. Ser. Prep. 3466) ; just as the homologous 

 structures in the human subject form a hernial protrusion into the cavity of the 

 uterus, which may persist as a more or less elevated area for several years. (Cf. 

 Robin, Mem. Imp. Acad. Med., torn, xxv., p. 137.) 



3. The homologue of the saucer-shaped deciduous serotina of the Rat is, in the 

 human subject, the thin layer of laminated albuminous tissue, which, in a placenta 

 • xpelled without suffering much violence, is seen clothing its uterine surface. It 

 is smaller, relatively, to the other structures concerned in the nutrition of the foetus, 

 in the human than in any other species. It is more easily demonstrable in the 

 Monkey (Macacus Nemestrinus, e. g.), as being a more coherent and stouter 

 membrane than in Man. It is, however, here still a condensed and mem- 

 branous structure, as compared with its pulpy homologues in Camivora, Insectivora, 

 and Rodents. 



■i. In early periods of utero-gestation in the common Shrew and Hedgehog, the 

 deciduous serotina is a very much larger structure than the placenta proper, 

 which it entirely covers, except on the fcetal aspect. But in the Tenrec, near the 

 full time, the deeidua serotina is of but wafer-thickness. 



.*). Dr. Matthews Duncan and M. Robin have shown that the muscular coat of 

 the uterus is never left denuded after parturition in the human subject. The 

 same remark holds good in the case of the " deciduate " Mammalia, in all of which 

 a more or less modified mucous tissue, the " non-deciduous serotina,'' is left, after 

 parturition, upon the utero-placental area, from which the deciduous serotina and 

 placenta proper have been separated as "afterbirth." 



