ii8 Vertebrate Embryology 



the tail and lateral folds of the amnion. The 

 way in which these folds fuse together will be 



Fig. 38. C D — Diagrams illustrating the development of 

 THE fcetal membranes OF A BIRD. (After Parker and Haswell.) 



C, stage with completed amnion and commencing allantois. Z), stage in which 

 the allantois has begun to envelop the embryo and yolk-sac. The ectoderm and 

 entoderm are represented by black lines; the mesoderm is gray. 



a//, allantois. all', the same growing round the embryo and yolk-sac. 

 a vtt amnion, n m./^ a m./' ^ amniotic fold a n, anus. S r, brain. coei, 

 coelome. coei', extra-embryonic coelome. ^ /, heart, ins.ent^ mesenteron. 

 »«^/i, mouth, nch^ notochord. sp.cd, spinal chord, sr.irty serous membrane. 

 u iiib.d^ umbilical duct, vt.m, vitelline membrane, yk, yolk-sac. 



explained later, and will readily be understood 

 by study of Figs. 37 and 38. 



The formation of the allantois cannot readily 



