268 THE FIFTH DAY. [CHAP. 



body cavity which contain the lungs extending them- 

 selves ventrally round the outside of the pericardial 

 cavity. This process is illustrated by Fig. 88, taken 



Fm. 88. 



/. c. 



SECTION THROUGH AN ADVANCED EMBRYO OF A RABBIT TO 

 SHEW HOW THE PERICARDIAL CAVITY BECOMES SUR- 

 ROUNDED BY THE PLEURAL CAVITIES. 



ht. heart, pc. pericardial cavity, pl.p. pleural cavity. Ig. lung. 

 al. alimentary tract, ao. dorsal aorta, ch. notochord. rp. 

 rib. st. sternum, sp.c. spinal cord. 



from an embryo rabbit. The two dorsal sections of the 

 body cavity (pl.p.) finally extend so as completely to 

 envelope the pericardial cavity (pc.), remaining how- 

 ever separated from each other below by a lamina ex- 

 tending from the ventral wall of the pericardial cavity 



