a VASCULAR SYSTEM eves! 
manner. On each side, the longitudinal commissural vessel, 
which connects the ventral ends of the arterial loops surrounding 
the different gill-clefts, gives origin to a series of pairs of short 
transverse vessels, and by their union these combine to form a 
median longitudinal hypobranchial artery which lies beneath the 
ventral aorta. From the hypobranchial artery are derived the 
coronary arteries for the heart; and from the same artery, or 
from its lateral connexions with the longitudinal commissural 
artery, and, in the case of the hyoidean hemibranch, from the 
mandibular artery, are derived the various nutrient vessels for 
the gills. 
The arteries for the trunk, and for the pectoral and pelvic limbs, 
arise In succession from the dorsal aorta. The first of the series 
is the subclavian artery, which has its origin from the aorta close 
to the dorsal extremities of the fourth pair of epibranchial arteries. 
Each subclavian artery gives off a brachial artery to the pectoral 
fin, and is then continued forwards as a lateral hypobranchial 
artery, which, with its fellow of the opposite side, eventually 
becomes continuous with the hinder end of the median hypo- 
branchial artery. Behind the subclavian artery there is a 
median coelaco-mesenteric artery, the various branches of which 
are distributed to the liver, stomach, and intestine. A lieno- 
gastric artery supphes the pancreas and spleen, and also sends 
branches to the stomach. In addition, there are also arteries for 
the gonads, numerous segmental arteries for the myotomes, and 
renal arteries for the kidneys. Finally, the aorta gives off a 
pair of iliac arteries for the pelvic fins, and then enters the haemal 
canal as the caudal artery. 
The more important differences in the arterial system of the 
Holocephali and the Teleostomi relate to (1) the absence of the 
posterior efferent branchial artery in each branchial arch; (2) 
modifications dependent on the condition of the spiracular and 
hyoidean hemibranchs, and the mode of origin and the course of 
their afferent and efferent vessels; and (5) the source from 
whence the air-bladder derives its blood when that organ is 
present. 
(1) The branchial arterial system is somewhat more primitive 
than in the generality of Elasmobranchs.! There are no complete 
vascular loops round the gill-clefts, and the blood from the two 
1 Cf. footnote to p. 332. 
