18/5.] Mr. W. Turner on the Placentation of Hyrax. 153 



placental zone removed along with the chorion, but for some distance on 

 each side of the zone the mucosa tore away from the muscular coat of 

 the uterus. 



The fcotal surface of the placenta was smooth, and on it the umbilical 

 vessels ramified before entering the villi of the chorion. Some injection 

 was passed into them, but it did not flow into their intra villous branches. 

 The uterine surface of the artificially separated placenta was flocculent ; 

 and the flocculi were seen, on microscopic examination, to consist of 

 bundles of connective tissue intermingled with corpuscles, obviously the 

 submucous connective tissue of the placental zone. 



A toughish membrane, continuous on each side with the mucosa of the 

 non-placental area of the uterus, could without difficulty be peeled off the 

 uterine surface of the placenta as a well-defined layer. When examined 

 microscopically, the surface of this membrane which lay next the uterus 

 was seen to resemble in structure the flocculi projecting from it ; whilst 

 the part next the placenta was much more abundantly cellular, and 

 stained readily with carmine. The surface which had been in apposition 

 with the placenta was irregularly undulating, and divided into numerous 

 shallow crypt-like recesses, separated from each other by raised folds of 

 the membrane. These crypts were lined by a layer of cells, the nuclei 

 of which were very distinct. I regard this membrane as the serotina, or 

 modified uterine mucosa of the placental zone ; whilst the crypts, with 

 their epithelial lining, are the closed ends of the deep pits in which 

 the villi of the chorion are lodged. 



The substance of the placenta was then examined, with the object of 

 determining not only the form of the foetal villi, but if prolongations of 

 the maternal mucosa passed into the placenta between the villi. In ver- 

 tical sections the villi appeared as if simple filamentous structures, 

 extending from the chorion to the crypt-like recesses in the serotina ; but 

 when portions of the placenta were teased out with needles, so that the 

 villi were not injured, although an occasional simple villus was seen, the 

 majority were broad, sinuous, leaf-like villi, with bud-like offshoots at 

 the free border, such as I have described and figured in the domestic 

 cat (Trans. Eoy. Soc. Edinburgh, 1875). In horizontal sections through 

 the placenta the sinuous outline of the villi presented so close a resem- 

 blance to the cat, that it was difficult in this particular to distinguish 

 Hyrax from Felis. Under a magnifying-power of 320 diameters, a layer 

 of flattened cells, the nuclei of which were almost circular and bright 

 with transmitted light, was seen at the surface of the villus. Intermingled 

 with the foetal villi were laminar prolongations of the maternal mucosa, 

 which invested and closely followed the sinuosities of the villi, similar to 

 the arrangement I have described and figured in the domestic cat*. 

 This intraplacental maternal tissue was present not only in those sections 



* Memoir " On the Placentation of the Seals," already cited, 1875, p. 293, pi. xxi. 

 flg. 14. 



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