34S HIKUTA : OX THE SEllO-AMXIOTIC CONXECTIOÎf, 



In some individuals a peculiar triangular sheet is observed at the 

 anterior end of the connection (Fig. 11). This is due to the following 

 circumstance. The anterior ])art of the connection (jften obtains a 

 considerable dorso-ventral extension, and thus produces a triangular 

 sheet whose base corresponds to its anterior free edge, and whose 

 sides correspond to the lines along which it joins respectively the 

 amnion and the serous envelope (Fig«. 11 and 79. Figs, (i and 70). 

 This triangular sheet does not stand edgewise, but (-(jmes to lie on 

 its surface and hence is seen from outside, as in Fig. 11. 



Thus, the mesoblastic bridge, which is supposed by all writers 

 on the embryology of the chick U) be absorbed, making the extra- 

 embryonic coelomic cavity continuous from one side to the other, 

 is in reality greatly widened and remains to the last day of the 

 incubation. 



7. Verforaiion in the Mcsohlaslic Connection. 



From the eleventh day, the plate-like connection begins to be 

 perforated here and there by numerous round and elliptic ]:)ores, which 

 ]nit the amniotic caA'ity in communication with the space outside the 

 serous envelope, so that the plate is now changed into a sie^e, and the 

 epiblast of the amnion and that of tlie serous envelope again become 

 continuous. This state of the connection is represented in Figs. 

 ol-5o. Each of these figures is of a view from inside the amnion, 

 part of which is represented in circular outline (Amn.) ; a tube- 

 like structure attached to this piece of the amnion is a part of the 

 alliumen sac which is lined by the serous envelope. How the albu- 

 men sac has assumed such a shape will be explained fully farther 

 on. It is represented as tilled with a l^lue mass. The membrane 

 which separates the amniotic cavity from that of the allîumen sac is 

 the sero-amniotic connection. It has nuiny ))erf ^rations which con- 



