. Outlines of zoology. Zoology. S34 AMPHIBIA. processes, and a short neural spine. The eighth vertebra has a biconcave or amphicoelous centrum. The ninth is convex in front, with two convex tubercles behind, and bears large transverse pro- mx cesses with which the hip- girdle articulates. The uro- style, formed by the fusion of several vertebras, has anteriorly a dorsal arch enclosing a prolongation of the spinal cord; but both arch and nerve-cord soon #/ disappear posteriorly. The notochord, around which the vertebral column has developed, is finally repre- sented only by the vestiges in the
. Outlines of zoology. Zoology. S34 AMPHIBIA. processes, and a short neural spine. The eighth vertebra has a biconcave or amphicoelous centrum. The ninth is convex in front, with two convex tubercles behind, and bears large transverse pro- mx cesses with which the hip- girdle articulates. The uro- style, formed by the fusion of several vertebras, has anteriorly a dorsal arch enclosing a prolongation of the spinal cord; but both arch and nerve-cord soon #/ disappear posteriorly. The notochord, around which the vertebral column has developed, is finally repre- sented only by the vestiges in the centra of the vertebrae. The skull consists—(a) of the persistent parts of the original cartilaginous brain- box or chondrocranium, de- veloped, as in the skate, from parachordals and trabecular, plus nasal and auditory Fig. 227.—Skull of frog—upper and capsules ; (/>) of ossifications pJrkerSUrfaCe'- '^^ W' K' °f PartS °f the chondr°- ' cranium, cartilage bones ; (c) Upper surface— c , ° . ' Pmx., premaxiiia; n., nasal; m., ot membrane or investing bones; and (d) of associ- ated visceral maxilla; Sg., squamosal; ,, quad- rato-jugal; , ex-occipitaI&; parieto-frontals ; , spheneth moid; , pro-otic. Lower surface— Pmx., premaxiiia; M., maxilla; quadrato-jugal; Q., quadrate; Pt. pterygoid ; Ps., parasphenoid ; pro-otic ; , sphenethmoid ; Pi. palatine ; V., vomer ;. c, columella. Two ex-occipitals bounding the foramen magnum and forming the condyles, two pro-otics or ossi- fications of the original auditory capsule, and an unpaired spheneth- moid forming the front of the brain-case, are cartilage bones. Probably the slender rods known as quadrato-jugals or jugals are also cartilage bones. Two parieto-frontals and two nasals above, a paired vomer and an unpaired dagger-shaped parasphenoid beneath, and two lateral hammer- shaped squamosals aie membrane bones. There is no basisphenoid Please note th
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
