FROM TWELVE TO THIRTY-SIX SOMITES 



209 



Fig. 120). A more complete description of the cavities is given 

 in Chapter XI. 



The median wall of the pleural grooves forms much mesobla.st 

 during the formation of the lung diverticula, and thus initiates 

 the formation of lobes enclosing the lungs (Figs. 118 and 119). 

 These lobes descend ventrally and unite with the septum trans- 

 versum (see below), thus producing blind bays of the coelome 



nX,-. 



^<5Y. 



/?ec/' 



jris-tdor^- 



stom. 



'/v'a't.irQTl. 



/ 



Fig. 119. — Transverse section of the same embryo through the 



lateral mesocardia. 



Liv., Liver, m's'c. lat., Lateral mesocardiiim. m's't. access., 

 Accessory mesentery, m's't. ven., Ventral mesentery. Other 

 abbreviations as before. 



at the sides of the oesophagus, known as the superior recesses 

 of the peritoneal cavity or pulmo-enteric recesses. 



The ventral mesentery extends from the anterior end of the 

 sinus venosus to the hind end of tlie fore-gut, where it unites 

 with the ventral body-wall. It includes the sinus venosus and 

 the ductus venosus, together with the hepatic diverticula. The 

 median and lateral mesocardia, together with the ventral mesen- 

 tery of the fore-gut, form a mass known as the septum transversum. 



