THE HUMAN EMBKYO. 



along which the allantoic vessels can pass from the embryo to 

 the placenta (Fig. 198, AA, VA) ; and the explanation of the pre- 



FIG. 254. A diagrammatic section of the pregnant Human Uterus at the 

 seventh or eighth week. (From Quain's ' Anatomy,' after Allen Thomson.) 



al, allantoic stalk, am, true amnion ; the part shaded horizontally, between the 

 amnion and the embryo, is the amnionic cavity, c, cavity of the uterus, c', plug of 

 mucus in the cervix uteri. c7i, chorion. d?-, decidua reflexa. d.i, decidua serotina. dv , 

 decidua vera. i, intestine of embryo, u, allantoic arteries, y, yolk-sac, y', yolk-stalk. 



cocious appearance of the allantoic stalk, and probably also of 

 the peculiarities of its development, in human embryos, is to 

 be found in the importance of establishing vascular relations 



