VI.] 



THE PKOCTOD^EUM 

 FIG. 61. 



175 



DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POS- 

 TERIOR END OF AN EMBRYO BIRD, AT THE TIME OF THE 

 FORMATION ON THE ALLANTOIS. 



ep. epiblast; Sp.c. spinal canal ; ch. notochord ; n.e. neurenteric 

 canal ; hy. hypoblast ; p.a.g. postanal gut ; pr. remains of 

 primitive streak folded in on the ventral side ; al. allantois ; 

 me. mesoblast ; an. point where anus will be formed ; p.c. 

 perivisceral cavity ; am. amnion ; so. somatopleure ; sp. 

 splanchnopleure. 



does not last long, but even after its rupture there re- 

 mains a portion of the canal continuous with the gut ; 

 this, however, constitutes a purely embryonic and tran- 

 sient section of the alimentary canal, and is known 

 as the postanal gut. Immediately in front of it is a 

 deep infolding of the epiblast, which nearly meets the 

 hypoblast (Fig. 61, an) and forms the rudiment of the 

 anus and of the outer section of the cloaca into which 

 the bursa Fabricii opens in the adult. It is known to 

 embryologists as the proctodceum, but does not open 

 into the alimentary tract till considerably later. The 



