On the Female Organs and Placentation of the Racoon. 289 



clearly enough defined. It consisted of closely applied, flattened 

 endothelial scales, which at some places were of an oval form, whilst 

 at others they were fusiform in character. As seen in transverse 

 sections, the vessels, doubtless because of their strongly elastic walls, 

 were observed to be uniformly open. They were in some cases com- 

 pletely, and in others partially filled by a granular looking material, 

 which doubtless consisted of altered blood-corpuscles,. In the latter 

 case the vascular contents had shrunk away from the wall of the 

 vessel, leaving a clear space between them and the endothelial lining 

 of the tube. The vessels were imbedded in a matrix of faintly 

 fibrillated connective tissue, which, however, was small in quantity, 

 and in some places appeared to be altogether wanting. At these 

 places, the vessels lay directly in contact with one another. 



It is worthy of remark, that the colossal capillaries just described 

 constituted by far the larger mass of the placenta, and that in this 

 portion of the organ there was an almost complete absence of 

 capillaries of the usual description, these being confined to the circum- 

 papillate ridges, and their prolongations, which I regard as constituting 

 the maternal portion of the organ. 



Having now described the histological appearances of what I regard 

 as the foetal portion of the placenta, I pass to the consideration of 

 that of the maternal part. I have already shown that each of the 

 papillee met with on the uterine surface of the placenta was sur- 

 rounded by a well-defined wall of tissue which bounded a space, in 

 the centre of which the papilla was situated. The papilla? consisted 

 exclusively of a mass of colossal capillaries, together with a small 

 amount of inter- vascular connective tissue matrix. An examination 

 of the circum-papillate ridges with a simple lens showed that these 

 were merely the free edges of a number of elongated processes which 

 dipped into the substance of the placenta. With a little care these 

 ridges, together with their intra-placental prolongations, could readily 

 be drawn out from the substance of the placenta and submitted to 

 microscopic examination. After being teased out and placed under the 

 microscope with a magnifying power of 440 diameters, these processes 

 were seen to present exactly the same structure as the mucous mem- 

 brane of the impregnated horn of the uterus, of which, without doubt, 

 they were prolongations. They consisted of a slightly fibrillar connec- 

 tive tissue largely intermingled with clear granular cells resembling 

 leucocytes, together with numerous spindle-shaped connective tissue 

 corpuscles. Moreover, in certain preparations which I was fortunate 

 enough to procure by simply drawing out the processes in question 

 from the placental substance, I was able to observe that the surfaces 

 of the latter were covered with a layer of columnar epithelial cells, 



* " Trans. Eoy. Soc. Edin.," vol. xxvii, p. 71. 



