222 MISS M. POOLE ON THE DEVELOPMENT OF THE  [ Mar. 2, 
wall of the posterior air-sac. From an examination of the earlier 
stages, however, it is evident that the dorsal component of the 
post-hepatic septum is really formed by the whole of the more 
posterior portion of the post-pulmonary septum, with its contained 
air-Sacs. 
Text-figs. 32, 33, and 34 also show those peritoneal cavities, 
called by Butler the ventral liver-sacs, in which the two liver- 
Text-fig. 32. 
tly 
thon: 
Adult Rook bisected horizontally through the region of the gizzard and liver-lobes, 
and slightly dissected anteriorly to expose the lungs; seen from the ventral 
side. 
lobes are seen to lie upon opening a bird from the ventral side. 
These are clearly formed by no special development of septa, but 
are simply those parts of the peritoneal cavity which, by the ventral 
attachment to the body-wall of the post-hepatic septum, become 
shut off anteriorly between this septum and the posterior wall of 
