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 cephalically an unpaired condition of the 

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



In the liver region the ventral mesentery does not disappear. 

 The liver 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 



ventral pancreas 

 dorsal pancreas 

 primary dorsal mesentery 



yolk stalk 



stro- hepatic omen turn 

 stomach 



large intestine 



aUantoic stalk 



(peritoneal region) 



FIG. 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 

 liver 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 accomplished by the formation of 



