

393 
The Morphology of the Ungulate Placenta, particularly the 
Development of that Organ in the Sheep, and Notes upon the 
Placenta of the Llephant and Hyrax. 
By RicHarp AssHETON, M.A., Lecturer on Biology in the Medical School of 
Guy’s Hospital, University of London. 
(Communicated by A. Sedgwick, F.R.S. Received April 18,—Read 
June 8, 1905.) 
(Abstract.) 
The formation of the placenta of the Ungulata vera is founded on a system 
of foldings of the subzonal membrane (or of the trophoblast only), which 
fit into corresponding grooves in the walls of the uterus, without thickening 
of the trophoblast layer of the blastocyst, and without destruction of 
maternal epithelium or other tissue (Sus). Certain parts of the crests of the 
ridges are produced by local amplification into true vill, into which the 
splanchnopleure of the allantois subsequently extends (Zquus, Bos, etc.). 
For this type of placentation, which is caused fundamentally by the 
folding of the trophoblast, the term plicate is used (placenta plicata), and to 
this type of placentation it is suggested that the Cetacea, Sirenia, and 
Proboscidea conform, as well as the Ungulata vera, and possibly the Edentata 
and Prosimia. 
The term placenta cumulata is used for the type of placentation in which 
the placenta is formed by the heaping up or thickening of the trophoblast 
layer, among the cells of which accumulation extravasated maternal blood 
circulates. Destruction of the maternal epithelium probably always occurs. 
To this type belong the Rodentia, Insectivora, the Hyracoidea, Primates 
Chiroptera. The Carnivora are perhaps intermediate, but, according to 
Strahl’s account, they would be distinctly plicate, while, according to the 
account of other authors, they are slightly cumulate. 
The morphological position of the Sheep’s placenta, a full account of the . 
development of which is given in the paper, is at that end of the series of 
plicate forms which closely approximates to the cumulate type. 
Though essentially plicate in mode of development, a slight tendency to a 
heaping up of the trophoblast occurs, in which a distinction into a plasmodi- 
trophoblast and a cytotrophoblast can be detected. The uterine epithelium 
is destroyed over certain areas in an early stage of pregnancy, and the 
plasmoditrophoblast forms a layer of cells, which has been mistaken for a 
