a.tr. 



FIG. 100. Formation of the amnion in the rabbit. (After van Beneden, from 

 Jenkinson's Vertebrate Embryology, Oxford, at the Clarendon Press.) 



h.am, Head amnion fold ; (.am, tail amnion fold ; c, embryo ; all, allantois ; a.tr, 

 allantoidean trophoblast ; i/.s, yolk-sac ; o.tr, omphaloidean trophoblast ; 

 c, extra-embryonic coelom ; s.t, sinus terminalis of area vasculosa. 



FIG. 101. Foetal membranes of horse, later stage. (After Bonnet, from 

 Jenkinson's Vertebrate Embryology, Oxford, at the Clarendon Press.) 



<, Villus ; ep.th, epithelial thickenings of amnion ; h, hippomanes ; am.c, 

 amniotic cavity ; all, allantois ; y.s, yolk-sac. 



