236 



FCETAL MEMBRANES. 



sack the folds of the amnion meet and coalesce above the 

 embryo (fig. 147, 3 and 4, am). After this the inner or true 

 amnion becomes severed from the outer or false amnion, 

 though the two sometimes remain connected by a narrow stalk. 

 Between the true and false amnion is a continuation of the body 

 cavity. The true amnion consists of a layer of epiblastic epithe- 

 lium and generally also of somatic mesoblast, while the false 

 amnion consists, as a rule, of epiblast only ; though it is possible 

 that in some cases (the Rabbit ?) the mesoblast may be con- 

 tinued along its inner face. 



Before the two limbs of the amnion are completely severed, 

 the epiblast of the umbilical vesicle becomes separated from the 

 mesoblast and hypoblast of the vesicle (fig. 147, 3), and, to- 



FIG. 147*. DIAGRAM OF THE FCETAL MEMBRANES OF A MAMMAL. 



(From Turner.) 



Structures which either are or have been at an earlier period of development 

 continuous with each other are represented by the same character of shading. 



pc. zona with villi; ss. subzonal membrane; E. epiblast of embryo; am. amnion; 

 A C. amniotic cavity ; M. mesoblast of embryo ; H. hypoblast of embryo ; UV. 

 umbilical vesicle; al. allantois; ALC. allantoic cavity. 



gether with the false amnion (s/i), with which it is continuous, 

 forms a complete lining for the inner face of the zona radiata. 



