288 PROFESSOR ROLLESTON ON THE 



which a watch-shaped cavity is included, and each of which is sieve-hke centrally from 

 vascular perforations. 



The placenta (PI. L. fig. 1) is thinnest at its centre ; at its periphery the chorion is 

 prolonged upwards in the shape of a circular rim (ch') of a depth of a quarter of an inch. 

 The umbilical vessels are very plainly seen to be prolonged into ramifications along this 

 rim, and in it. The rim itself, or upgrowth, is continuous with the parapet, or down- 

 growth, of uterine mucous membrane (u p, PI. L. fig. 3) — an arrangement which, so far 

 as 1 have been able to find, is unique. 



The umbilical cords of these foetuses are long ; the foetuses being about an inch and 

 a half long, the cord is in some instances of equal length with them ; and the cavity of 

 the amnios is large — sufficiently capacious, indeed, to admit of the introduction of a 

 second foetus. Resembling the Human foetus more or less in these two points, the foetal 

 membranes of the Tenrec resemble those of the Ruminants in the possession of numerous 

 corpuscles studding the interior surface of the amnios. These corpuscles are in some 

 cases attached to the inner surface of the amnios, but in most cases they have fallen 

 away from it ; in some cases they are filiform or even club-shaped, in most they are boat- 

 shaped, or, rather, of the shape of a single valve of an ordinary bivalve, and attached 

 by the concave side to the amnios, whilst projecting with a smooth convex one into iis 

 cavity. And as to the naked eye, so under the microscope, they resemble les plaques 

 de I'amnios chez les Ruminants, as described by Professor Claude Bernard'. The longer 

 of these corpuscles were as much as two millimetres long by one broad — much the same 

 size, in fact, as the similarly placed corpuscles of the Elephant described by Professor 

 Owen^; many, however, were of smaller dimensions. 



I could not discover any traces of yelk-sac, nor of allantois, nor of any membrane 

 exterior to the amnios. Neither were any omphalo-mesenteric vessels detectable within 

 the cavity of the abdomen. But the anastomosis between the veins of the abdominal 

 wall and the umbilical vein, which is not rare in Mammalia'', was very plainly demon- 

 strable. 



The placenta proper has assumed the " flocculent " appearance which prolonged 

 maceration, whether in weak spirits or in any other such menstruum, will confer on any 

 placenta, however " cellulo- vascular" or " spongy," in the normal condition. Still to the 

 apices of its villus-bearing trees, shreds of the lamina (fig. 2) are in several instances 

 left adhering, especially in the angle between the chorionic upgrowth, ch', and the 

 uterine aspect of the placenta. The layer of tissue adherent to the utero-placental area 

 possessed histological characters quite distinct from those of the muscular coat it over- 

 lay. The circular muscular coat is easily separable from the longitudinal. 



The lamina of tissue (fig. 2) intermediate between the placenta and the utero-placental 

 area, I would propose (without any reference to the etymological meaning of the word 



' Brown-Scquaid. 'Journal de Physiologie,' vol. ii. p. 34, 1859. ' Phil. Trans. 1857, p. 348. 



' Rathke and Coste, cit. KoUiker, ' Entwickelungsgeschichte,' p. 420. 



