HUMAN PHYSIOLOGY 



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p 1G 4 9> DEVELOPMENT OF THE FCETAL MEMBRANES OK A MAMMAL. 



(After Kolliker.) 



I, ovum with zona pellucida, blastula, and embryonic area; 2, formation of 

 yolk-sac and amnion; 3, union of the folds of the amnion, forming the amniotic 

 cavity; formation of the allantois; 4, decrease of the yolk-sac, increase of the 

 allantois, formation of mouth and anus; 5, reduction of the yolk-sac; allantois 

 joined to the chorion, enlargement of the amniotic cavity; </, zona pellucida; </', 

 processes (villi) of zona; sh, serous membrane; sz, villi; ch, chorion, c/iz, chori- 

 onic villi; am, amnion; As, head-fold of amnion ; a/i, amniotic cavity; as, navel- 

 cord with the amnion; aa', ectoderm; ?', endoderm; mm' , mesoderm; dd, embry- 

 onic part of the endoderm; df, area vasculosa; sf, sinus terminalis; kk, cavity of 

 the blastula; ds, umbilical vesicle (yolk-sac); dg, passage of the umbilical vesicle; 

 at, allantois; e, embryo; r, space between chorion and amnion; vl, ventral body 

 wall; ////, pericardial cavity. 



