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Show 1 9 0 5 .] PLACENTA OF THE SPINY MOUSE. 2 81 Each horn had been opened. Opposite the slit on the meso-metric side a swelling 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. The fcetus of Acomys cahirinus, together with the placenta separated from the wall> 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 tliin membrane could be seen covering cei'tain 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 mm. 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 ^ At the point where the cord appears to penetrate the sac there |
