^os^^Wi 



Fig 364 (A) Transverse section of the thoracic area of opossum embryo showmg 

 the separation of the parietal pericardium from the lateral body walls by expanding 

 pleural sacs. (The preparation from which this drawing was made was loaned to the 

 author by Dr. J. A. McClain.) (B-1 ) Transverse section through lung buds and pleural 



870 



