256 



DIFFUSED PLACENTA. 



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

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

 the Ungulata. 



cli 



FIG. 160. DIAGRAM OF THE FCETAL MEMBRANES IN ORCA GLADIATOR. 



(From Turner.) 



ch. chorion; am. amnion; al. allantois; E, embryo. 



Manis. Manis amongst the Edentata presents a type of diffused pla- 

 centa 1 . 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, ,1 may quote the following sentence from Turner 

 (Journal of Anat. and Pkys., vol. x., p. 706). 



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

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

 gymnurus, recently described by Kolliker 2 , had a transversely oval placenta, 

 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 

 mucosa. 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." 



Lemuridae. 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 cornua 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 chorion are numerous vascular villi, which fit into 

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



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. 



2 Entwicklungsgeschichte des Menschen, etc., 2nd ed., p. 362. Leipzig, 1876. 



