. A manual of zoology. Zoology. IV. VERTEBRATA: AMPHIBIA. 513 MONOPNEUMONIA, with One swim bladder: Ceratodus, Australia. Dipneu- MONIA, witli two bladders: Proloptenis, Africa; Lepidosiren, South America. The larvas of both have four pairs of gills, three of which are retained in Protop- lenis. Possibly the paleozoic Arthrodira, some of gigantic size (Diniclithys), belong here. Class III. Amphibia. There are two views as to the origin of the Amphibia. According to one they have descended from Crossopterygian ganoids; the other is that they have come from the Dipnoi. The class is distinguished
. A manual of zoology. Zoology. IV. VERTEBRATA: AMPHIBIA. 513 MONOPNEUMONIA, with One swim bladder: Ceratodus, Australia. Dipneu- MONIA, witli two bladders: Proloptenis, Africa; Lepidosiren, South America. The larvas of both have four pairs of gills, three of which are retained in Protop- lenis. Possibly the paleozoic Arthrodira, some of gigantic size (Diniclithys), belong here. Class III. Amphibia. There are two views as to the origin of the Amphibia. According to one they have descended from Crossopterygian ganoids; the other is that they have come from the Dipnoi. The class is distinguished at once from the fishes by the absence of fins. There is, it is true, a median fin in larval life, and this may persist (Perenniljranchs, Triton), but it is never divided into dorsal, caudal, and anal, and it lacks any skeletal support (figs. 4, 5). The paired fins are replaced by toed feet (p. 464). These are often webbed and are used for swimming, for creeping and leaping, and are consequently jointed between the separate skele- tal elements (fig. 564). Besides the shoulder and hip joints, which alone occur in fishes, there occur also elbow (knee), wrist (ankle), and finger joints. The number of digits is not always five, for a reduction to four, three, or even two occurs. The connexion of the girdles with parts of the axialeskeleton (lacking in most fishes) is of impor- tance. The pelvic girdle is connected with the vertebral column by means of the ilium, which arti ulates either directly or by a sacral rib with the single sacral vertebra. Ventrally the two halves of the girdle fuse, and usually the limits of ischium and pubis cannot be traced. The attachment of the pectoral girdle is less firm (fig. 521, A). The dorsal portion, the scap- ula, ends free in the muscles; the ventral, differ- entiated into coracoid and clavicle, either meets the opposite side in a symphysis {firmislernous Anura) or the two sides overlap {arciferous Anura and urodeles). A connexion with the ver
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
