35 G HIEOTA ; OX THE SERO- AMNIOTIC CONNECTION, 



shows the extent of the cave. The line at which the cave comes in 

 contact with the amnion represents the sero-amniotic connection. 



Tlie two lobes of the allantois that overlap do so with their accom- 

 panying serous envelope, so that there ought to be sheets of epiblastic 

 cells between the lobes, witli the mesoblast and the hypoblast lining 

 them. In point of fict, it becomes impossible to distinguish these 

 layers, and only a simple septum, whose nature is not clear, divides 

 the cavities of the two allantoic lobes. The epiblastic sheet is visible 

 only near the outer limit of the septum (Fig. 82). In future I shall 

 call this the ' Inter allantoic Septum.'' It has a free edge aloug which 

 the allantoic vein runs, and is, for the time, somewhat heart- 

 shaped. At tliis stage other two minor interallantoic septa are 

 formed by the right and left allantoic arteries in their respective lobes 

 (Fig. 12). These are much smaller than the primary septum but in 

 other respects show no essential difference. The amniotic cavity 

 is now much enlarged and the yolk-sac much reduced. In fact, it 

 is at this stnge that the epiblastic sero-amniotic l)ridge has become 

 ahnost entirely replaced by the mesoblastic tissue. Fig. 12 represents 

 the surface view of the foetal membranes on the ninth day and Fig. 

 13 the vicinity of the sero-amniotic connection. In this particular 

 example the amniotic cavity is drawn out towards tlie connectiou, 

 and the cave (Fig. 13 DABC) is narrower and longer than that in 

 Diag. 8. 



With further growth, the amniotic cavity becomes enlarged, the 

 yolk and the albumen-sac diminished, the allantois extended, and the 

 interallantoic septum widened. Through these changes, occun-ing 

 simultaneously, the foetal membranes reach in later days a degree of 

 complexity, which well nigh defies description. 1 will only atteiii})t 

 here to explain the arrangement of the foetal membranes in an embryo 

 of the tenth day by means of several figures and diagrams which are 



