. Outlines of zoology. Zoology. CETACEA. 705 Bunodont, and Phenacodus as near the origin of the horse stock. But Pkenacodus is so generalised that Cope has suggested affinities between it and not only Ungulates, but also Carnivores and Lemurs. The tertiary strata of S. America have yielded a number of strange types, , Toxodon, Nesodon, and Typotherium, ranked in the sub- orders Toxodontia and Typotheria. From the Eocene of N. America, Marsh has disentombed a group of animals which he calls Tillodontia, , Tillotherium, which seem to combine the characters of the Ungulata, Rodentia, and
. Outlines of zoology. Zoology. CETACEA. 705 Bunodont, and Phenacodus as near the origin of the horse stock. But Pkenacodus is so generalised that Cope has suggested affinities between it and not only Ungulates, but also Carnivores and Lemurs. The tertiary strata of S. America have yielded a number of strange types, , Toxodon, Nesodon, and Typotherium, ranked in the sub- orders Toxodontia and Typotheria. From the Eocene of N. America, Marsh has disentombed a group of animals which he calls Tillodontia, , Tillotherium, which seem to combine the characters of the Ungulata, Rodentia, and Carnivora. Order 4.—Cetacea. The Cetaceans, including whales and dolphins and their numerous relatives, are aquatic mammals of fish-like form. The spindle-shaped body has no distinct neck between the relatively large head and the trunk, and tapers to a notched tail, the horizontal expansions of which form the flukes. The fore limbs are paddle-like, and there are no external hints of hind limbs. Most forms have a median dorsal fin. Hairs are generally absent, though a few bristles may persist near the mouth. The thick layer of fat or blubber beneath the skin serves to retain the warmth of the body, and thus compensates for the absence of hair. In one of the dolphins dermal ossicles occur, a fact which has suggested the idea that the toothed whales may have had mailed ancestors. Traces of dermal armour have also been found in the extinct Zeuglodonts. The general shape, the absence of external ears, the absence of an eye-cleansing nictitating membrane, the dorsal position and valvular aperture of the single or double nostril, the sponginess of the bones, the retia mirabilia in different parts of the body, may be associated with the aquatic life of these mammals. 45. Fig. 258.—Left fore-limb of Balnenoptera. Sc, Scapula with spine {sp): H., humerus; R., radius; U., ulna; C., carpals embedded ir matrix ; Mc., metacarpals ; Ph., Please note that these images are extra
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
