. Outlines of zoology. Zoology. CHELONrA. 563 sented by the Galapagos lizard, which swims out among the sea-weed; by some estuarine crocodilians; by some turtles which live far out at sea, and only seek the shores to lay their eggs ; and by the sea-snakes (Hydrophidse), which never leave the water. •r Chelonia. Tortoises and Turtles. General Characters.—The body is compact and broad in the region of the trunk. There is a dorsal and a ventral shield, within the shelter of which the head and neck, tail and lifnbs, can be more or less retracted. The dorsal carapace is usually formed from—(a) the.
. Outlines of zoology. Zoology. CHELONrA. 563 sented by the Galapagos lizard, which swims out among the sea-weed; by some estuarine crocodilians; by some turtles which live far out at sea, and only seek the shores to lay their eggs ; and by the sea-snakes (Hydrophidse), which never leave the water. •r Chelonia. Tortoises and Turtles. General Characters.—The body is compact and broad in the region of the trunk. There is a dorsal and a ventral shield, within the shelter of which the head and neck, tail and lifnbs, can be more or less retracted. The dorsal carapace is usually formed from—(a) the. Fig. 241.—External appearance of tortoise. flattened neural spines (plus dermal bones); (b) expanded and more or less coalesced ribs {plus dermal bones ; (c) a series of dermal marginal bones around the outer edge. In the Athecce the dorsal vertebra and ribs are not fused to the dermal plates which form the carapace. The ventral shield or plastron is formed of nine or so dermal bones. There is no sternum. Overlapping, but in no way corresponding to the bony plates, are epidermic horny plates of " tortoise shell" which, though very hard, are not without sensitiveness, numerous nerves ending upon them. The quadrate is immovably united with the skull. The jaws are covered by a horny sheath, and are without teeth, though hints of these have been seen in some embryos. The average life of Chelonians is sluggish. Perhaps this is in part due to the way in which the ribs are lost in the. 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 Thomson, J. Arthur (John Arthur), 1861-1933. Edinburgh, Glasgow and London, H. Frowde and Hodder & Stoughton
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
