DEVELOPMENT OF THE CHICK SECOND PEEIOD. 315 



the anterior is now called the vagina capitis ; the posterior va- 

 gina caudcB (fig. 343, B, f, backwards) ; the lateral folds may, 

 in like manner, be entitled the vaginae later ales (fig. 343, A, 

 /, /) ; they coalesce at the end of the fourth day, and form a 

 visible cicatrice over the lumbar region of the embryo. In this 

 way we have a complete vesicular envelope thrown around the 

 embryo, the AMFION (fig. 344, a, a), which is filled with 

 fluid. The upper layer of the fold (fig. 343, A and B, lying 

 under the vitelline membrane, a\ covers the whole germinal 

 membrane, and grows around the yolk as a serous capsule or 

 cyst, vesica serosa the false amnion of Pander. At the place 

 where the embryo lies, this layer is separated from the rest of 



Fig. 344. Outline of the embryo of the fowl, at the end of the fifth 

 day, much magnified ; a, a, amnion ; 6, allantois ; c, corpora quadrige- 

 mina ; d, hemispheres ; e, eye ; /, anterior ; and g, posterior extremity. 

 The natural dimensions of this, as of many of the other figures, are indi- 

 cated by a line, or lines, with an asterisk. 



