1905. | PLACENTA OF THE SPINY MOUSE. 281 
Each horn had been opened. Opposite the sht on the meso- 
metric side a swelling marked the place of attachment of the 
fully formed placenta and fetus in the one case, and of the 
absorbed specimen in the other. 
The feetus 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 foetus of Acomys cahirinus, together 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 fetus. 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 1s 
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 (feetal) 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 
