388 CHORDATA. 
In comparing this arrangement with that of the pigeon, we 
notice the absence of renal portals and a different relation- 
ship of the posterior veins caused by the backward extension 
of the kidneys in the latter. Hence there is nothing in the 
rabbit approaching the ‘‘renal cycle” of the pigeon. 
The arterial system has two parts. The pulmonary 
system consists of a pair of large but short pulmonary 
arteries leading from the right ventricle to the lungs. The 
left pulmonary artery is connected with the dorsal aorta by 
a transverse vessel, the ductus arteriosus. (Plate XIII.) 
It is only functional in the embryo, becoming a solid band 
in the adult. 
The systemic system consists of two main arteries which 
separate soon after emergence from the left ventricle. The 
vight innominate runs forwards and outwards, and divides 
into the right carotid to the head and right subclavian to 
the fore-limb and shoulder. The aorta bends forwards and 
outwards to the left, and gives off a eft carotid to the head, 
then a left swéclavian, and is continued backwards to the 
left of the mid-dorsal line through the diaphragm which 
it supplies by a small phrenic artery breaking up on the 
surface of the diaphragm. It lies dorsal to the postcaval 
to the hind-end of the body where it comes round and lies 
ventral to it. It gives off a median unpaired ce/ac to liver, 
stomach and spleen, anterior mesenteric to the intestine and 
pancreas and posterior mesenteric to the rectum, paired renads 
and genitals to kidneys and genital organs, and then divides 
into two common iliacs which give off zio-lumbars and in 
turn bifurcate into femoral and internal tac. The persist- 
ence of the 4/t aortic arch alone instead of the right, as in 
the pigeon, should be noted. Again, there is only one 
(right) innominate artery, the left carotid and subclavian 
communicating directly with the dorsal aorta instead of 
forming a separate left innominate, as in the pigeon. It 
will be remembered that in the frog the subclavians (or 
brachials) come off from the aortic arch on each side, so 
that the rabbit must be regarded as the more primitive in 
having only one innominate. However, the arrangement 
of carotids and subclavians varies very much throughout 
the AZammata. Lastly, the very close correspondence 
of the arterial and venous system is striking. With the 
