[Illustration: FIG. 198.—The branchial circulation in _Lepidosteus_ (diagrammatic). _a_, _a_, Afferent branchial arteries; _c_, carotid; _d.a_, dorsal aorta; _e_, _e_, efferent branchial arteries; _ef.a_, efferent vessel from the hyoidean gill which, after its union with the hyoidean artery, becomes the afferent vessel of the spiracular pseudobranch; _ef.a′_, efferent vessel of the spiracular pseudobranch; _hy.a_, hyoidean artery; _hy.g_, hyoidean gill; _sp.ps_, spiracular pseudobranch; _v.a_, ventral aorta; 1-5, the hyo-branchial and succeeding gill-clefts. (After F. W. Müller and Ramsay Wright.)] In this Fish the efferent branchial vessels open dorsally into right and left suprabranchial arteries,[385] which unite behind to form a median dorsal aorta (Fig. 199). Anteriorly, the paired suprabranchial arteries extend towards the base of the skull as the so-called "carotid" arteries. The two carotids enter the cranial cavity, and there unite in the median line, as in the Cyclostomes. By the union of these arteries in front, and of the {337}right and left suprabranchial arteries behind, the characteristic "circulus cephalicus" of Teleosts is completed.[386] From the anterior part of the cephalic circle are derived two internal carotid arteries[387] for the brain, and also a pair of orbito-nasal arteries for the eye-muscles and the nasal sacs, while more posteriorly an external carotid has its origin from each suprabranchial artery. [Illustration: FIG. 199.—Branchial arterial system of the Cod (_Gadus morrhua_). Lateral view. _af.b.a_, First afferent branchial artery; _cl.a_, coeliac artery; _d.a_, median dorsal aorta; _ef.b.a_, first efferent branchial artery; _ex.c_, external carotid; _H_, heart; _hy.a_, hyoidean artery; _Hy.b.a_, hypobranchial artery for the heart and pelvic fins; _hy.ps_, spiracular pseudobranch; _in.c_, internal carotid;[387] _l.d.a_, left suprabranchial artery; _m.a_, mesenteric artery; _on_, orbito-nasal artery; _oph.a_, ophthalmic artery; _r.d.a_, right suprabranchial artery; _sb.a_, subclavian artery; _v.a_, ventral aorta; 1-5, hyobranchial and succeeding gill-clefts. (Altered from T. Jeffery Parker.)] (3) In most Teleostomi the air-bladder is supplied with blood by branches of the coeliac artery, with the addition of small branches arising directly from the dorsal aorta. _Polypterus_ and _Amia_[388] are, however, exceptional, inasmuch as the arteries for the air-bladder are derived from the last or fourth pair of efferent branchial vessels, and in this respect, but not in the destination {338}of the corresponding veins, the two genera exhibit a significant resemblance to the Dipnoi. In the Dipnoi the ventral aorta is so short that the afferent branchial arteries arise almost directly from the conus arteriosus with their roots in close contiguity to one another (Fig. 200).