STRUCTURE OF FOUR-DAY CHICKS 



153 



lomic chambers become confluent to form the pericardial 

 region of the body cavity (Figs. 24 and 55). Later in develop- 

 ment the ventral mesentery farther caudally disappears so that 

 caudally as well as cephahcally an unpaired condition of the 

 coelom is brought about (Fig. 54, H). 



In the Hver region the ventral mesentery does not disappear. 

 The Hver arises as an outgrowth from the gut and in its develop- 

 ment extends into the ventral mesentery (Fig. 54, G). The 

 portion of the ventral mesentery dorsal to the liver persists as 



Pig. 55. — Schematic lateral view of dissection of four-day chick to show the body- 

 cavity and the more important mesenteries. 



the gastro-hepatic omentum, and the portion ventral to the 

 Hver persists as its ventral ligament (falciform ligament) 



(Fig. 55). 



The primary dorsal mesentery persists and forms the sup- 

 porting membranes of the digestive tube. In the adult its 

 different regions are named according to the parts of the digest- 

 ive tube with which they are associated, as for example, meso- 

 gaster that part of the primary dorsal mesentery which suspends 

 the stomach, mesocolon, that part of the primary dorsal mesen- 

 tery supporting the colon, etc. 



The separation of the body cavity into pericardial, pleural, 

 and peritoneal chambers is accompHshed by the formation of 



