GENERAL HISTORY OF THE EMBRYO. 



365 



body, to which the yolk-stalk is attached, remains in the same 

 position as before, the head and neck, which have greatly in- 

 creased in size, are bent downwards at right angles to the trunk, 

 and, pushing down the wall of the yolk-sac before them, appear 

 to project into this latter : the head and neck are, however, 

 really separated from the cavity of the yolk-sac, as shown in 

 Fig. 147, by the wall of the sac itself. The hinder or tail end 

 of the embryo, the basal part of which is alone shown in 



FlG. 147. — A Rabbit Embryo and blastodermic vesicle at the end of the tenth 

 day. The embryo is represented in surface view from the right side, the 

 course of the alimentary canal being indicated by the broad dotted line ; 

 the blastodermic vesicle is shown in median longitudinal, or sagittal section. 

 The greater part of the tail, which in the natural condition is twisted 

 spirally, has been removed. (In part after Van Beneden and Julin.) x 10. 



AW, proamnion. AX, amnionic cavity, between the inner or true amnion and the 

 embryo. C, extra-embryonic part of the coelom or body-cavity. E, epiblast. E', thickened 

 epiblast, by which the blastodermic vesicle is attached to the uterus, and from which the 

 foetal part of the placenta is formed. EI, auditory vesicle. EK, cpiblastic villi. GF, fore- 

 gut. GH, hind-gut. G-T, mid-gut. H, hypoblast. OL, lens of eye. R, heart. SI, sinus 

 terminalis. TA, cavity of allantois. YS, cavity of yolk-sac or blastodermic vesicle. 



Fig. 147, has also grown considerably, and is wrapped spirally 

 round the stalk of the allantois. 



By the twelfth day the embryo has acquired the form shown 



