. A manual of zoology. Zoology. IV, VERTEBRATA: MAMMALIA, CETACEA 571 Order X. Cetacea. In form the whales rescmljle the sircnians, a result of an aquatic life, but the resemblance ends here. The whales are so fish-like that every one speaks of the whale fishery. Head and trunk are scarcely distinguished, the cervical vertebra; being very short and more or less completely fused. The hind limbs are absent, of the pelvic girdle only a small ilium remains, and no sacral vertebra; are developed. The caudal fin differs from that of a fish in being horizontally flattened; the skin is thick and is sp
. A manual of zoology. Zoology. IV, VERTEBRATA: MAMMALIA, CETACEA 571 Order X. Cetacea. In form the whales rescmljle the sircnians, a result of an aquatic life, but the resemblance ends here. The whales are so fish-like that every one speaks of the whale fishery. Head and trunk are scarcely distinguished, the cervical vertebra; being very short and more or less completely fused. The hind limbs are absent, of the pelvic girdle only a small ilium remains, and no sacral vertebra; are developed. The caudal fin differs from that of a fish in being horizontally flattened; the skin is thick and is sparsely haired or comjJetely naked, some lacking hair even in the embryo. Tilijst of the species inhabit the high seas, Inia boUviensis and Platanisla gangetica occur in rivers. The fore limbs are modified into flij)pcrs, the bones of wliicli are of nearly equal size and are jointed only at the shoulder. A dorsal fin ('fin backs') occurs in some. The lack of hair is compensated by the thick layer of subcutaneous fat (blubber). In order that the animals may breathe while feeding, the larynx is prolonged into a tube which extends up through the pharynx to the choana;, from which the nostrils extend directly upwards to the single (Denticetes) or paired (Mysticetes) external opening. Since the air expelled contains much moisture and this is condensed on contact with the cooler external air, the im- pression was natural that the animals in 'blowing' spouted water. As the olfactory membrane is degenerate and the olfactory lobes are reduced, the nose is an organ of respiration Fig. 619.âSection through jaws of whalebone whale (after Delate), c, septum of nose; m mouth cavity; mx, maxillary bone; p, (hinder end); v, vomer; â w. baleen. The eyes are small, external ears are lacking, the mammse are dose to the sexual opening. The teeth are either present in large numbers, similar and conical and, since the second dentition is rudimentary, are monophyodont (Denticetc
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
