3i6 



CHORD AT A. 



are lined by a peritoneum or thin membrane and contain i 

 colourless coelomic fluid. The coelom communicates by th( 

 abdominal pores with the exterior. The peritoneum sur 

 rounds all the organs in the abdominal cavity, and the 



Fig. 227. — Diagram of Arterial System of a Skate. 



Seen from Ventral Surface. 



External 



Carotid. 

 Internal Carotid, 



Hyoidean, 



Anterior 



Innominate. 



Posterior 

 Innominate. 



Caudal. 

 The afferent branchial system is shaded darker than the rest. 



oesophagus and rectum are suspended from its dorsal wall 

 by a mesentery^ formed of two folds of peritoneum apposed ; 

 the part of the alimentary canal between these two has no 

 mesentery and lies freely in the cavity. Another fold, the 

 omentum^ contains the bile-duct and portal vein. 



