ON THE ARRANGEMENT OF THE FCETAL MEMBRANES IN THE CETACEA. 499 



The placenta is distinctly subdivided into two portions, a maternal and a 

 foetal. The maternal consists of the specially modified uterine mucous mem- 

 brane, in which, from the attached to the free surface, the following parts may 

 be recognised : — The utricular glands c, imbedded in the connective tissue, and 

 surrounded by an open capillary plexus ; and the crypt layer, consisting of a, 

 cup-shaped crypts, and b, funnel-shaped crypts, into the latter of which the 

 utricular glands c. open. In this crypt layer are found the connective tissue 

 (including the fusiform corpuscles d, and the layer of spheroidal sub-epithelial 

 corpuscles e e) and the close capillary plexus g g ; the crypts are lined by 

 the epithelial layer //. The foetal portion consists of the chorion, from 

 which the villi h h project and fit into the crypts of the maternal part of the 

 placenta. These villi are invested by the epithelial layer i i, and they consist 

 of connective tissue which contains a layer of sub-epithelial corpuscles k, of 

 fusiform corpuscles I, and a close capillary plexus m m, derived from the 

 umbilical arteries, which plexus is continued into an extra-villous chorionic 

 network n n, from which the umbilical vein arises. The foetal and maternal 

 vessels are not in contact, still less continuous, with each other, but are 

 separated by the layer of sub-epithelial corpuscles of the villus, the epithelial 

 investment of the villus, the epithelial lining of the crypt, and the layer of sub- 

 epithelial corpuscles of the crypt. The space between the two epithelial surfaces 

 is intended to show the interval between the foetal and maternal portions into 

 which the secretion of the uterine glands is poured. 



It may be useful to compare the above diagram with the well-known diagrams 

 with which Professors John Reid* and Goodsir have illustrated their views of 

 the structure of the human placenta. By both these anatomists the tufts of 

 foetal villi were regarded as intimately related to the dilated uterine sinuses, 

 the inner coat of which, or a structure continuous with that inner coat, being 

 reflected on to each tuft. But Goodsir also represented two systems of cells : — 

 The external cells of the villus, belonging to the decidua, which lay in imme- 

 diate relation to the foetal aspect of the lining membrane of the maternal sinus ; 

 the internal cells which lay within the villus between its vascular loop and its 

 external membrane; and he separated the two systems of cells from each other 

 by a space which he regarded as the cavity of a secreting follicle, of which the 

 external cells were the secreting epithelia.t The human arrangement, as repre- 



* Edinburgh Medical and Surgical Journal, January 1841; and Physiological and Anatomical 

 Researches, p. 325. Edinburgh, 1848. 



■f* Although from the description ■which Professor Goodsir gave of these external cells, he 

 undoubtedly considered them to be of the nature of secreting epithelium, yet he did not represent them 

 in his diagram as situated on the free surface of the maternal placenta, but as separated from the space 

 between the maternal and foetal portions by a sharp line, as if a membrane intervened. How far he 

 intended this line to represent a definite structure I am unable to say. If such were his intention, then 

 the external cells would rather correspond in position to my layer of sub-epithelial corpuscles of the mucous 

 membrane than to a free epithelium. Similarly his layer of internal cells of the villus corresponds in 

 position, not to the epithelial investment, but to my layer of sub- epithelial corpuscles of the villus. 



VOL. XXVI. PART II. 6 



