. On the anatomy of vertebrates [electronic resource] . unite to form the(aortic circle, fig. 321, whichencompasses the basisphenoid, current of arterialised bloodflows forward at the fore-part ofthis circle into the hyo-oper-cular, e, and orbito-nasal, b,arteries ; but the main streamsare directed backward, and con-verge in the direction of thearrows to the aortic trunk. The carotids, c, the homologues of thesubclavians, d, sent to the pectoral fins, and sometimes the coro-nary vessels of the heart, are sent off from the aortic circle. Butno systemic heart or rudiment of a propelling rec
. On the anatomy of vertebrates [electronic resource] . unite to form the(aortic circle, fig. 321, whichencompasses the basisphenoid, current of arterialised bloodflows forward at the fore-part ofthis circle into the hyo-oper-cular, e, and orbito-nasal, b,arteries ; but the main streamsare directed backward, and con-verge in the direction of thearrows to the aortic trunk. The carotids, c, the homologues of thesubclavians, d, sent to the pectoral fins, and sometimes the coro-nary vessels of the heart, are sent off from the aortic circle. Butno systemic heart or rudiment of a propelling receptacle is de-veloped in any fish at the point of confluence of the branchialveins. Small vessels are sent off from marginal branchial venulesby short trunks, which ramify beneath the branchial membrane,and become the c arteriae nutritive of the gills: their capillariesare collected into venous trunks, which quit the gills commonlyat both their extremities, those from the dorsal ends joiningthe jugular veins, those from the ventral ends emptying. Commencement of Systemic Circulation,{Oadus Callarias). xxv. 1 XXV. i i 2 484 ANATOMY OE VERTEBRATES. themselves into the prsecavals, or directly into the great Such is the outline of the general structure of the beautifuland complex mechanism of the normal or pectinated gills of this there are many minor modifications; some of which receiveexplanation from known phenomena in the developement of thegills;2 others, teleogically, from the habits of the species. Five branchial arches and arteries, or vascular hoops, aredeveloped on each side in the embryo of all fishes above the Der-mopteri, as a general At first the trunk of the branchialarteries simply bifurcates, the divisions passing round the pharynx and reuniting on its dor-sal surface, to form theaorta. Behind this pri-mary circle, which cor-responds with the folddeveloping the hyoid andmandibular arches, fouradditional arterial hoopsare sent
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Keywords: ., bookcentury1800, booksubject, booksubjectbirds, booksubjectfishes
