230 



EMBRY0L0GICAL TYPES 



to each side, and forms the notochord in the middle line as 

 it retreats towards the hind end of the embryo. Neural folds 

 rise up and enclose the neural tube, and the embryo becomes 



ram 



Fig. i 10. — Diagram showing the relations of the embryonic membranes and 

 placenta of the rabbit, as seen in an idealised transverse section of the 

 uterus. (From Jenkinson, after Duval and van Beneden.) 

 all, allantois ; c, extra-embryonic ccelom ; ep, epithelium of the uterus ; 



hi, cavity of the uterus ; m, mesometrium ; otr, omphaloidean trophoblast ; 



pi, placenta (allantoic) ; pr am, proamnion ; ys, yolk-sac. 



folded up from the surrounding tissue by the head-fold and 

 tail-fold. In this way, the gut begins to be formed, and, 

 as in the chick, anterior and posterior intestinal portals arise 

 (see p. 21 1). 



