. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 484 ANATOMY OP VERTEBRATES. themselves into the prtecavals, or directly into the great aiiricnlar sinus.* Such is the outline of the general structure of the beautiful and complex mechanism of the normal or pectinated gills of fishes. Of this there are many minor modifications ; some of which receive explanation from known phenomena in the developement of the gills; ^ others, teleogically, from the habits of the species. Five brancliial arches and arteries, or vascular hoops, are developed on each side in the embryo of a
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 484 ANATOMY OP VERTEBRATES. themselves into the prtecavals, or directly into the great aiiricnlar sinus.* Such is the outline of the general structure of the beautiful and complex mechanism of the normal or pectinated gills of fishes. Of this there are many minor modifications ; some of which receive explanation from known phenomena in the developement of the gills; ^ others, teleogically, from the habits of the species. Five brancliial arches and arteries, or vascular hoops, are developed on each side in the embryo of all fishes above the Der- mopteri, as a general rule.^ At first the trunk of the branchial arteries simply bifurcates, the divisions passing round the pharynx and reuniting on its dor- s'2 sal surface, to form the aorta. Behind this pri- mary circle, which cor- resi)onds with the fold developing tlie liyoid and mandibular arches, four additional arterial hoops. are sent off, fig. ;'22 Eiuln-j'o Osseous Fi^li â I, n, wliicli traverse, without further ramifications, the couA'cx side of the four anterior simple Ijranchial arches, and reunite above in the aortic trunk, ib. in. If a sixth arterial arch be developed, correspond- ing with the fitth branchial arch, as its presence in the Le2n- dosiren would indicate, it has not been observed, and must soon disappear in most Osseous Fishes. In these the gills make their appearance as leaflets budding out from the con\exity of the four anterior branchial arches, each leaflet supporting a corresponding loop of the branchial artery ; and, as the bifur- cation and extension of the primary leaflets and the pulhilation of secondary laminje and loops proceed, the vascvilar arch Ijcgins to scj)arate itself lengthwise into two channels, traversed by ojiposite currents, and therel)y establishing an arterial, fig. 318, d, and a venous, ib. c, trunk in relation to the loops and their vascular developcments on tlie branchial processes. In Osseous Fi
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
