1909. ] SUBDIVISIONS OF THE BODY-CAVITY IN BIRDS. 213 
Text-fig. 25 isa slightly diagrammatic reconstruction from longi- 
tudinal horizontal sections of a chick of six days’ incubation, seen 
from the ventral side. The pericardium and heart, the ventral 
part of the alimentary canal, and all the liver except the most 
dorsal corner of the right lobe have been removed. 
Text-fig. 25. 
\ 
Sp.rnl. 
Slightly diagrammatic reconstruction from horizontal longitudinal sections of a 
chick of 6 days’ incubation ; seen from the ventral side. The pericardium 
and heart, the ventral part of the alimentary canal, and all the liver except 
the most dorsal corner of the right lobe have been removed. 
At this stage the two pairs of intermediate air-sacs first make 
their appearance, lying —together with the posterior air-sacs which 
are developed even earlier—in the ventral pulmonary ligaments. 
The pronephric folds are now seen, supporting the Miillerian ducts 
