GADUS., 335 
kidneys it divides into two renal portals, as in the skate ; the left renal 
portal breaks up into capillaries in the left kidney, but the right is 
usually continuous forwards with the right cardinal vein. A branch 
from the caudal vein, the ves¢cudar vein, runs ventralwards and joins 
the mesenteric branch of the Zorta/ vein. 
The portal system is well developed and consists of a mesenteric 
vein from the intestine, a splenic from the spleen and a branch from 
the air-bladder leading to the liver. The blood from the liver is carried 
by paired Aefazzc veins into the sinus venosus. 
Fig. 237.—LATERAL ViEw or Cop’s SKULL. 
4., Branchiostegal Rays. 2,, Lacrymal. .0., Preoperculum. 
c.4., Ceratohyal. mm, Maxilla. g-, Quadrate. 
d, Dentary. 2., Nasal. 5.0., Supraoccipital. 
#., Frontal. o, Operculum. s.0., Suboperculum 
4.m., Hyomandibular. p.s., Parasphenoid., (lower reference). 
z.0., Interoperculum. p.m., Premaxilla. 
The vascular system shows a peculiar asymmetry of both the arterial 
and venous systems, and a marked tendency to anastomosis of certain 
outlying vessels, seen also in the bird. Both the veins and arteries are 
remarkably small compared with the size of the fish, and there is a very 
small quantity of blood. 
Skeletal The skeleton of the cod is in marked contrast to that 
"of the skate in consisting almost entirely of bone. 
AXxIAL.—The [skull is formed of a cranium, mainly bone, and a 
series of bony visceral arches. The cranium is formed of (1) an occipital 
