316 CHORDATA. 
are lined by a peritoneum or thin membrane and contain a 
colourless coelomic fluid. ‘The ccelom communicates by the 
abdominal pores with the exterior. The peritoneum sur- 
rounds all the organs in the abdominal cavity, and the 
Fig. 227.—D1aGRAM OF ARTERIAL SYSTEM OF A SKATE. 
Seen from Ventral Surface. 
External 
Carotid. 
Internal Carotid. 
Anterior 
Innominate. 
Hyoidean. 
Posterior 
I Innominate. 
zZ 
ES) 
Gills. 
Subclavian. 
Efferent 
Branchials 
Hepatic. Be 
‘Ventral Aorta. 
Duodenal. 
Gastric. 
F Ceeliac. 
Anterior. 
Mesenteric. 
Genital. 
Posterior. 
Mesenteric. 
Renals. 
Tliac. 
Caudal. 
The afferent branchial system is shaded darker than the rest. 
cesophagus 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. 
