318 CHORDATA. 
column till it terminates in the caudaZ It gives off a median 
celiac to the stomach, a superior mesenteric to the spleen, 
pancreas and intestine, paired vena/s to the kidneys and 
paired z/acs to the pelvic fins. These arteries are fully 
exposed by removal of the coracoid bar and, if necessary, 
the pubic bar. 
We may note some special features of the blood-vascular 
system of the skate which are also typical of the class. The 
blood-vascular system can be divided into the arterial and 
the venous system as in all Vertebrata, but the venous system 
Fig 228.—DIAGRAM OF THE VENOUS SYSTEM OF A SKATE. 
Sinus 
Venosus. 
Hepatic Sinus. Jugular. 
Brachial. 
Hepatics. : 
Cardinal. q 
Genital. 
~ Renal. 
Lateral. 
Renals. 
Caudal. 
is chiefly composed of wide sinuses (also a common condi- 
tion of invertebrates). The arterial system has two distinct 
parts separated by the capillaries of the gills. The ventral 
or afferent branchial system carries venous blood forwards to 
the gills; the dorsal or efferent branchial system carries 
blood mostly éackwards to the system. In the venous 
system the capillaries of the liver and those of the kidney 
both break up the continuity of the sinuses, forming a 
hepatic-portal and renal-portal system respectively. 
