266 



THE FIFTH DAT. 



[chap. 



septum however is soon continued forwards so as com- 

 pletely to separate the ventral pericardial and the 

 dorsal body cavity in front, the pericardial cavity ex- 

 tending considerably further forwards than the body 

 cavity. 



Fig. 87. 



Section through the Caudiac Region op an Embryo op 

 Laceria Muralis of 9 m.m. to shew the mode 01? 



FORMATION OF THE PERICARDIAL CaVITT. 



lu. heart, pc. pericardial cavity, al. alimentary tract. Ig. lung. 

 I. liver, pp. body cavity, md. open end of MuUerian duct. 

 wd. Wolffian duct. vc. vena cava inferior, ao. aorta, ch. 

 notochord. mc. medullary cord. 



Since the horizontal septum, by its mode of origin, 

 is necessarily attached to the ventral side of the gut, 

 the dorsal part of the primitive body space is, as we 

 have already mentioned, divided into two halves by 

 a median vertical septum formed of the gut and its 



