286 



Dr. M. Watson. 



scope, there was observable a total absence of anything like a clearly- 

 defined, limitary membrane on the papillary surface. Consequently, 

 in sectional views, the papillae were indistinctly isolated from one 

 another, although as observed in surface views, the separation was 

 clearly enough denned. Here and there, but extremely rarely, an 

 isolated columnar epithelial cell was seen to be attached by its narrow 

 end to the papillar surface. Whether the uterine surface of the organ 

 had been invested by a continuous layer of these cells, or whether 

 those seen had been detached from the uterine mucous mem- 

 brane, I was unable to decide. In view, however, of the fact that 

 the uterine mucous membrane was entirely devoid of such cells, the 

 latter supposition appears the more probable. The trenches between 

 the papillae, as well as those between the latter and the surrounding- 

 ridges above described, were, to a considerable extent, filled with 

 numerous shreds of decidua, as well as by a quantity of blood cor- 

 puscles which presented various forms, due doubtless to the action of 

 the spirit in which the parts had been preserved. It was particularly 

 observed, that no vessel of large size, and presenting the structure 

 which I believe to be characteristic of those constituting the foetal 

 portion of the placenta, extended beyond the uterine surface of the 

 placenta. The marginal band of decidua reflexa presented the same 

 structure as that of the mucous membrane of the impregnated uterine 

 horn, to be afterwards described. 



The foetal surface of the placenta was clearly defined in sectional 

 views by the allantoic membrane. From this membrane numerous 

 septa were given off: at nearly regular intervals, and penetrated the 

 substance of the placenta, so as to form, as it were, supports for the 

 blood-vessels forming that organ. These placental septa could occa- 

 sionally be traced as continuous structures nearly as far as the uterine 

 surface of the placenta, but, for the most part, they disappeared before 

 reaching the latter. In either case, they gradually became more 

 delicate, and were finally lost to sight in the convolute of placental 

 blood-vessels. 



On proceeding to examine the blood-vessels composing the placenta, 

 I found that these presented two distinct types of structure, according 

 as I examined those which constituted the papillae, or those which 

 were met with in the circum-papillate ridges above described. In 

 view of the facts which I am about to communicate, I regard the 

 circum-papillate ridges as the torn margins of those processes of 

 maternal tissue which interpenetrate the foetal villi, whilst the papillae 

 themselves are simply the free extremities of the foetal villi, which in 

 the racoon, as in the bitch,* and cat,f reach the uterine surface of the 

 placenta. The vessels met with in the maternal portion of the 



* Turner, " Lectures on the Comparative Anatomy of the Placenta," p. 82. 

 t Ibid., p. 79. 



