. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. GILLS 357 As a rule Teleosts possess only four holobranchs,1 and this holds good for all Ganoids. A vestigial gill or pscudobranch is present on the anterior wall of the spiracle of many Elasmobranchs and of cartilaginous Ganoids (mandibular pscudobranch); the posterior hyoid hemibranch, which is functional in Acipenser and Lepi- dosteus, becomes more or less reduced in other Ganoids and Teleosts, forming the so-called opercular pseudobranch. Traces of. A B FIG. 263.—DIAGRAM ILLUSTRATING THE MECHANISM or RESPIRATION IN TE
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. GILLS 357 As a rule Teleosts possess only four holobranchs,1 and this holds good for all Ganoids. A vestigial gill or pscudobranch is present on the anterior wall of the spiracle of many Elasmobranchs and of cartilaginous Ganoids (mandibular pscudobranch); the posterior hyoid hemibranch, which is functional in Acipenser and Lepi- dosteus, becomes more or less reduced in other Ganoids and Teleosts, forming the so-called opercular pseudobranch. Traces of. A B FIG. 263.—DIAGRAM ILLUSTRATING THE MECHANISM or RESPIRATION IN TELEOSTS. (After Dahlgren.) A, phase of inspiration; B, phase of expiration. In both figures the anterior oral part () represents a vertical section, and the posterior pharyu- geal part enclosing the gills (Kiemen) a horizontal section. The arrows indicate the direction of the water-current and pressure, and those passing through the walls of the oral cavity the expansion and contraction of the opercular apparatus. In A, the maxillary and mandibular valves are open, and the branchiostegal membrane closed : in B, this condition is reversed. a cleft, lying behind the functional branchial clefts, are found in the embryos of certain Fishes and Amphibians. All these facts indicate the presence of a more extensive branchial apparatus in ancestral forms. (For the sieve-like gill-rakers, cf. Figs. 261 and 262.) In the Lophobranchii the gills are replaced by tufted processes, and in many Teleostei certain accessory structures are developed in the posterior region of the branchial chamber by a modification 1 They may be reduced to three, or two, and even these may be more or less rudimentary. A A**. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, W. N. (William Newton),
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