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 mesoblast 
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 ccelome 
Fia. 119. — Transverse section of the same embryo through the 
lateral mesocardia. 
Liv., Liver. m/’s’e. lat., Lateral mesocardium. 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 the 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. 
