MAMMALIA. 213 



mous, and is dorsally in apposition with, and apparently coalesces with, 

 the chorion, and veiitrally covers the inner wall of the persistent allantoic 



cli 



FIG. 160. DIAGRAM OF THE FCETAL MEMBRANES IN OKCA GLADIATOR. (From Turner.) 

 ch. chorion ; am. amnion ; /. allantois ; E. embryo. 



sack. The chorion, except for a small area at the two poles and opposite 

 the os nteri, is nearly uniformly covered with villi, which are more nume- 

 rous than in fig. 160. In the large size of the aiunion, and small dimen- 

 sions of the persistent allantoic sack, the Cetacea differ considerably from 

 the Ungnlata. 



Manis. Manis amongst the Edentata presents a type of diffused 

 placenta'. The villi are arranged in ridges which radiate from a non-villous 

 longitudinal strip on the concave surface of the chorion. 



Manis presents us with the third type of placenta found amongst the 

 Edentata. On this subject, I may quote the following sentence from 

 Turner (Journal of Anat. and Phys., vol. x., p. 700). 



"The Armadillos (Dasypus), according to Professor Owen, possess a 

 single, thin, oblong, disc-shaped placenta; a specimen, probably Dasypus 

 gyrunurus, recently described by Kolliker 2 , had a transversely oval pla- 

 centa, which occupied the upper |rds of the uterus. In Manis, as Dr 

 Sharpey has shewn, the placenta is diffused over the surfaces of the chorion 

 and uterine niucosa. In Myrmecophaga and Tamandua, as MM. Milne 

 Edwards have pointed out, the placenta is set on the chorion in a dome- 

 like manner. In the Sloths, as I have elsewhere described, the placenta is 

 dome-like in its general form, and consists of a number of aggregated, 

 discoid lobes. In Orycteropus, as I have now shewn, the placenta is 

 broadly zonular." 



Lemurida3. The Lemurs in spite of their affinities with the Primates 

 and Insectivora have, as has been shewn by Milne Edwards and Turner, an 

 apparently very different form of placenta. There is only one embryo, which 

 occupies the body and one of the comua of the uterus. The yolk-sack 

 disappears early, and the allantois (Turner) bulges out into a right and 

 left lobe, which meet above the back of the embryo. The cavity of the 

 allantois persists, and the mesoblast of the outer wall fuses with the 

 subzonal membrane (the hypoblastic epithelium remaining distinct) to give 

 rise to the chorion. 



On the surface of the choiion are numerous vascular villi, which fit 

 into uterine crypts. They are generally distributed, though absent at the 

 two ends of the chorion and opposite the os uteri. Their distribution 



1 The observations on this head were made by Sharpey, and are quoted by Huxley 

 (No. 202) and with additional observations by Turner in his Memoir on the placenta- 

 tion of the Sloths. Anderson (No. 191) has also recently confirmed Sharpey 's account 

 of the diffused character of the placenta of Manis. 



3 Entwicklungxgeschichte rfc.s Mensrhcii, etc., 2nd od., p. :i(V2. Leipzig, 187(5. 



