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 hypobranchial artery. Behind the subclavian artery there is a median coeliaco-mesenteric artery, the various branches of which are distributed to the liver, stomach, and intestine. A lieno-gastric artery supplies 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 (3) 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.[380] There are no complete vascular loops round the gill-clefts, and the blood from the two {334}hemibranchs of each branchial arch is conveyed to the dorsal aorta by a single efferent vessel which corresponds to the more anterior of the two in _Mustelus antarcticus_.[381] (2) In _Callorhynchus_[382] among the Holocephali, where the spiracle is absent but the hyoidean hemibranchi is still a true gill, the latter organ is supplied with venous blood by a branch from the ventral aorta, the corresponding efferent vessel joining the dorsal aorta (Fig. 196). In the absence of a spiracular pseudobranch the anterior carotid may be regarded as continuous with the hyoidean artery,[383] and as having its origin directly from the efferent artery of the hyoidean hemibranch (Fig. 196). At its origin the anterior carotid anastomoses with the mandibular artery. [Illustration: FIG. 196.—Portion of the efferent branchial system of _Callorhynchus_. _a.c_, Anterior carotid; _a.cb.a_, anterior cerebral arteries; _d.a_, dorsal aorta; _ef.b.a_, 1-4, efferent branchial arteries; _ef.hy_, efferent artery from the hyoidean hemibranch; _hy.c_, hyobranchial cleft; _md.a_, mandibular artery; _my.a_, myelonal artery; _p.c_, posterior carotid; _p.cb.a_, posterior cerebral artery. (From T. Jeffery Parker.)]