. Chordate anatomy. Chordata; Anatomy, Comparative. THE SKELETAL SYSTEM 171 In elasmobranchs the number of visceral cartilages is reduced to corre- spond with the reduced number of gill apertures. The maximum number is nine, in Heptanchus, of which the first, the mandibular, is modified to become the cartilages of the upper and lower jaws, while the second arch, the hyoid, functions slightly as a gill arch, and its dorsal division, the hyomandibular cartilage, acts as a suspensory apparatus for the lower jaw. The dorsal division of the first visceral arch, which forms the cartilage of the uppe
. Chordate anatomy. Chordata; Anatomy, Comparative. THE SKELETAL SYSTEM 171 In elasmobranchs the number of visceral cartilages is reduced to corre- spond with the reduced number of gill apertures. The maximum number is nine, in Heptanchus, of which the first, the mandibular, is modified to become the cartilages of the upper and lower jaws, while the second arch, the hyoid, functions slightly as a gill arch, and its dorsal division, the hyomandibular cartilage, acts as a suspensory apparatus for the lower jaw. The dorsal division of the first visceral arch, which forms the cartilage of the upper jaw, is called the palato-pterygo-quadrate cartilage, since palatal, pterygoid, and quadrate bones develop from it in amphibians and reptiles. The lower half of the first visceral arch forms cartilage of the lower jaw, Meckel's cartilage. An articulation is formed between the two,. Fig. 161.—Branchial arches of (A) Heptanchus; (B) Chlamydoselachus; and (C) Cestracion. c, ceratobranchial; e, epibranchial; h, hyoid; hb, hyobranchial; he, hyoid copula; cbr, cardiobranchial (posterior copula); p, pharyngobranchial; 1-7, branchial arches; m, Meckel's cartilage. (A and C after Gegenbaur, B after Garman; from Kingsley's "Comparative Anatomy of ;) so that in elasmobranchs a biting mouth replaces the sucking mouth of cyclostomes. Nevertheless, the upper jaw does not fuse with the cranium in elasmobranchs but remains independent. Posterior to the hyoid arch, the visceral cartilages persist in elas- mobranchs as supports of the branchial or gill arches. The number is commonly reduced to five. Most teleosts have only four functional branchial arches, and in some the number is reduced to two. Perenni- branch amphibians have either two or three. Land animals have lost their gills entirely, but cartilaginous and bony skeletal supports persist and are turned to new and diverse uses. In Amphibia, both upper and lower jaw cartilages are at least in part converted into b
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