152 Mr. W. Turner on the Placentation of Hyrax. [Dec. 16, 



ubsequently (Comp. Anat. Vertebrates, iii. p. 742) states that the villi 

 are imbedded in a decidual substance, and the surface of attachment to 

 the uterus is less limited than in the elephant. Prof. Huxley, in his 

 Hunterian Lectures, 1863*, described the placenta of Hyrax as having 

 such an interblending of the foetal and maternal portions that it is as 

 truly deciduate as that of a rodent. In his ' Manual of the Anatomy of 

 Vertebrated Animals,' 1871, he further points out that the maternal 

 vessels pass straight through the thickness of the placenta towards its 

 foetal surface, that the allantois spreads over the interior of the chorion 

 and gives rise to the broad zone-like placenta, and that the yelk-sac and 

 vitello-intestinal duct early disappear. 



In direct opposition to the views of these anatomists, M. H. Milne- 

 Edwards has recently stated f that there is nothing in the placenta of 

 Hyrax to indicate the presence of a caduca, and the allantois does not 

 overstep the limits of the placental zone. The villi, he says, are mostly 

 simple, very* analogous to those of an ordinary pachyderm. In the 

 midst of the zone vascular vegetations are engaged in corresponding 

 uterine cavities, but they adhere no more than do the analogous prolon- 

 gations in the ruminant to the crypts in which they are included ; they 

 can be detached with the same facility without tearing through any thing, 

 and without carrying away any portion of uterine tissue. M. George, in 

 an elaborate monograph on the genus Hyrax, published in June last J, 

 figures not only the placenta, but the gravid uterus of this animal. He 

 says nothing, however, of the structure, which he was apparently pre- 

 cluded from examining, but adopts the view of M. H. Milne-Edwards that 

 it was non-deciduate. 



The antagonism between the views of the English and Erench ana- 

 tomists, not only as regards the structural details, but the conclusions as 

 to the nature of the placentation, has rendered it advisable to have the 

 placenta of Hyrax reexamined ; and, with great liberality, Prof. Huxley 

 has placed at my disposal his specimen, which had been preserved in 

 spirit of wine. I shall now describe what I have seen. 



The uterus was two-horned. Two well-developed ova, each about 

 3| inches long, were in one cornu. One ovum had been opened, the 

 membranes and placenta examined, and the foetus removed ; the other 

 ovum was entire. The placenta was zonary, and varied in different 

 parts of the zone from between J to | inch in breadth, whilst the average 

 thickness was -^ inch. The non-placental areas of the chorion were 

 smooth and translucent, and, as in the Carnivora, branches of the umbi- 

 lical vessels ramified in them. The zone on the chorion was intimately 

 blended with a corresponding zone in the uterine mucosa. When the 

 placenta was stripped off the uterus, not only was the mucosa in the 



* Elements of Comparative Anatomy, 1864, p. 111. 



t Considerations sur la Classification des Mammiferes, Paris, 1868. 



\ Annales des Sciences Naturelles, 1875. 



, 



