SEPTUM TRANSVEKSUM 



239 



the coelom from below. Between the lateral lobes on the dorsal aspect is a groove 

 in which the mesenteric partition is inserted. Into this partition the lung- 



~ x - 



\ 



en r it I' X. 



_- lateral 

 mesocardiitm 



r posterior 



mesocar<iii/>ii 



pericardium '" 



FIG. 293. FIGUKE OBTAINED BY COMBINING SEVERAL SUCCESSIVE SECTIONS OF A HUMAN 

 EMBRYO OP 7'5 MM. (FOURTH WEEK). (From Kollmann.) 



The arrow indicates the opening of the pleural cavity into the peritoneal. 



m.p.p. 

 r. duct of Cnvier \ w.f. d.p. 1. duct of Cuvier 



mitral pillar 



lorsal pillar 



ai)tero-lat<'>-nl recesx 



Woltfan fold _ 



coeliac artery 



Wolffianfold 



FKI. '294. MODEL OF A HUMAN EMBRYO OF 6'8 MM., SHOWING THE DORSAL WALL OF CCELOM. (After Piper.) 



.p'.p., membrana pletiro-peritonalis ; w.f., anterior end of Wolffian fold; d.p., dorsal pillar of 

 pleuro-peritoneal membrane. 



rudiments extend from before backwards, and encroach on the coelomic clefts. 

 The anterior part of the coelom of each side now becomes the primitive pleural 



