PLACENTAL STRUCTURES OF THE TENREC. 297 



that BischofF, who has figured what is nothing else than this primitive chorion (fig. 59, 

 Meerschweinchen-Ei), should have yet fallen into the error relative' to it which he has 

 done, and to which, as entailing yet another error, we shall have to revert. 



In both early and advanced embryo, the non-placental uterine mucous membrane 

 becomes continuous with the saucer-shaped deciduous serotina on its convex aspect, 

 about the eighth of an inch within a line corresponding with the periphery of the after- 

 birth, or, in other words, along a line concentric with, but an eighth of an inch within the 

 thickened band of the late embryo. The circular parapet by which the persistent and 

 deciduous uterine structures are connected is but a slight lamina, and gives way upon 

 very little traction. The blood-vessels and cellular tissue within its periphery serve 

 to keep the after-birth in continuity with the persistent non-deciduous serotina. Indeed, 

 in the Agouti the blood-vessels form the only bond of union, and the after-birth becomes 

 " pedunculate," at least if we may trust an observation put on record by Bischoff'^ as 

 made by Dr. Franz Miiller. On the other hand, the Guinea Pig's deciduous serotina 

 is, as shown in our figure 5, connected with the uterine non-placental mucous surface 

 by a series of tags (d s") or fimbriae, developed at its periphery, as well as with the non- 

 deciduous serotina by an abundance of vessels. These peripheral tags are most 

 distinctly continuous with the uterine walls, and are injectible from the uterine vessels, 

 whence it is much to be wondered at that BischofF [1. c. p. 42) should have spoken of 

 them as the remnants of the perfect decidua reflexa of earlier days. Our figure 6, and 

 the description appended to it, will show where the rudiment of that structure is really 

 to be sought for. These tags are to be seen in a fostal Rat, in Prep. 3467, Hunterian 

 Museum, and they are described as follows: — "The folds or processes of the lining 

 membrane of the uterus which converge to be attached to the maternal portion of the 

 placenta, are here shown." Their office is described to be that of " supporters of the 

 embryo and conductors of the vessels of the maternal placenta." With this description 

 my own of the homologous growths in the Guinea Pig will be seen to agree ; but I 

 should be inclined to say that in the preparation in question there is, besides the system 

 of radiating peripheral tags, also the uterine circular parapet, usually found alone in 

 the Rat, coexisting with them, though I have not been able to satisfy myself of the 

 coexistence of these two connecting media in any placenta, as that of the Guinea Pig, 

 which I have been able to manipulate. Neither have I ever been so fortunate as to 

 find this system of tags in the common Rat (Mus decumanus) ; and but that the homo- 

 logous structures, two only in number, which are to be seen in the Rabbit (Lepus cuni- 

 culus), and are figured and described in PI. L. figure 7, are far from being invariable in 

 their appearance, I should suggest that the foetal Rat in question was of the Black Rat 

 {Mus rattus) species. 



' KoUiker, /. c. pp. 160, 161, 1/2. 



2 'Meerschweinchen-Ei,' p. 6; Miiller, 'Wiener Zeitschrift,' 1851; Schmidt, ' Jahrbucher,' Bd. Ixi. 

 p. 329. 



