. A manual of zoology. Zoology. 514 CHORDATA The vertebral column often (rerennihranchs, Derotremcs, Carcilians, ami many Stej^ocephali) resembles that of fishes in amphiccclous centra and persistence of notochord. The notochord may disappear, there then occurring opisthocrelous (Salamandrina) or procaious centra (most Anura). There is also an articulation of skull with vertebral column, rare in fishes but characteristic of land animals, by which tlie first vertebra (atlas) becomes distinct from the rest. The skull is remarkal>le for the extent to which the chondrocranium is retained and th
. A manual of zoology. Zoology. 514 CHORDATA The vertebral column often (rerennihranchs, Derotremcs, Carcilians, ami many Stej^ocephali) resembles that of fishes in amphiccclous centra and persistence of notochord. The notochord may disappear, there then occurring opisthocrelous (Salamandrina) or procaious centra (most Anura). There is also an articulation of skull with vertebral column, rare in fishes but characteristic of land animals, by which tlie first vertebra (atlas) becomes distinct from the rest. The skull is remarkal>le for the extent to which the chondrocranium is retained and the consequent small number of primary bones (tigs. 565, 500). The bones of the orliilal region are represented by a pair each of all- and orl )itosphenoids in the urodeles, by a ring of bone, the spliciui/imoid, in the anura. The auditory region usually contains only prootics, the J^nsc. i (rK c'occ Fig. 565.—Frog skull from below (from WicJcrshcim). For letters sec fig. 566. occipital only exoccipitals. The absence of other occipitals is often of value in chstinguishing between amphibian and reptilian skulls, since in the former the articulation with the atlas is consec|uenlly by double occipital cojiJyIcs. Of secondarv cranial bones are to be mentioned the nasals, frontals (in many prefrontals also), and parietals, the latter two fused in anura to J'ronloparietals; ventrally tlie large parasphenoid. The cranium is increased by the addition of the large quadrate cartilage, which becomes applied to the otic capsule and (Anura) fuses with it, while the rest of its arch (pterygoid) extends forward in a more or less complete condition, reaching the nasal capsule in the Anura. The quadrate cartilage is covered externally by the squamosal and sujiports the lower jaw, composed of Meckel's cartilage surrounded by membrane bones (dentary, splenial, angulare, etc.); its. Please note that these images are extracted from scanned page images that may have been digitally enhanced for reada
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
