1905. 



PLACENTA OF THE SPINY MOUSE. 



281 



Each horn had been opened. Opposite the slit on tlie meso- 

 meti-ic side a sAvelling marked the place of attachment of the 

 fully formed placenta and foetus in the one case, and of the 

 absorbed specimen in the other. 



The foetus appeared devoid of amnion and was chiefly remarkable 

 for the long hairs or spines which rise from the dorsal walls of 

 the nostrils and point backwards over the head. The pits from 

 which these hairs arise are plainly visible (text-fig. 41). 



Text-fig. 41. 



rx\ 



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Tlie fa3tus of Acomys cahirinus, tog-ether with the placenta separated from the walls 

 of the uterus. The sac-like folds attached to the discoid placenta are the 

 yolk-sac and amnion membranes. An epitrichium is seen closely applied to 

 the body of the foetus. X 3. 



A thin membrane could be seen covering certain parts of the 

 embryo, the face, neck, and wrist, and it could be detected by 

 careful search over other parts. This membrane covered the 

 finer hairs, but was perforated by the stout bristles, and is 

 probably of the nature of an epitrichium. 



The foetus was attached by a long cord to the placenta, which 

 had been separated from the uterus. 



The placenta was discoidal in shape, but with a longer diameter 

 of 12 mm. and a shorter of 9-5 nun. In thickness it was about 

 3 mm. The embryonic surface was concave, the ab-embryonic 

 surface convex (text-fig. 42). 



Attached to the proximal (foetal) surface of the placenta was 

 a wide sac through which the cord passed to the centre of the 

 placenta. 



At the point where the cord appears to penetrate the sac there 



