FORMATION OF THE MEMBRANES 



803 



c'fc 



Fig. 224. Five diagrammatic representations of the formation of the membranes in mammalia 



(Kolliker). 



i: a, a', epiblast; d, vitelline membrane; d' ', villi on the vitelline membrane; i, hypoblast; m, m' , 

 mesoblast. 



2: a', external layer of the amnion ; d, d' , vitelline membrane; <?, embryo; ds, umbilical vesicle; f/, 

 ks, s s, folds of the amnion ; d d, m', s f, hypoblast ; d d, connection of the embryo with the um- 

 bilical vesicle. 



3: d,d', viteiline membrane; v /, internal amniotic layer; e, embryo; a h, amniotic cavity; s h, sh, 

 external amniotic layer; am, space between the two layers of the amnion; dd, hypoblast; df, s t, 

 i, walls of the umbilical vesicle ; dg, omphalo-mesenteric canal ; d s, cavity of the umbilical vesicle ; 

 a /, first appearance of the allantois. 



4: s h, external layer of the amnion; s z, villi of the external layer of the amnion, which has now be- 

 come the chorion, the vitelline membrane having disappeared; hh,am, internal layer of the am- 

 nion ; e, embryo ; a h, amniotic cavity ; dg, omphalo-mesenteric canal ; d s, cavity of the umbilical 

 vesicle ; a /, allantois ; r, space between the two layers of the amnion. 



5 : ch, s h, c h, a /, allantois (which has now become the chorion, the external amniotic layer having dis- 

 appeared) , with its villi ; a m, amnion ; a s, amniotic covering of the umbilical cord ; r, space between 

 the amnion and the allantois; ah, amniotic cavity; ds, umbilical vesicle; dg, omphalo-mesenteric 

 canal. 



