. The chordates. Chordata. nalia: Classification 76:5 Skin very thick and nearly devoid of hair; only one pail' of mam- mary organs, situated in extreme anterior (pectoral) region. Stomach complex, resembling that of artiodactyls. Brain relatively small and only slightly convoluted. Sirenians are the sea cows inhabiting the warmer coastal regions of the Atlantic, Pacific, and Indian Oceans and adjoining bodies of fresh water. They feed on aquatic vegetation. Length up to 8 or 10 feet. There are only two living Genera: Manatee (Trichechus or Manatus: Fig. 577): No incisors; only six cervical ve
. The chordates. Chordata. nalia: Classification 76:5 Skin very thick and nearly devoid of hair; only one pail' of mam- mary organs, situated in extreme anterior (pectoral) region. Stomach complex, resembling that of artiodactyls. Brain relatively small and only slightly convoluted. Sirenians are the sea cows inhabiting the warmer coastal regions of the Atlantic, Pacific, and Indian Oceans and adjoining bodies of fresh water. They feed on aquatic vegetation. Length up to 8 or 10 feet. There are only two living Genera: Manatee (Trichechus or Manatus: Fig. 577): No incisors; only six cervical vertebrae. Atlantic coastal regions of America and Africa. Dugong (Halicore): One pair of tusklike upper incisors; seven cervical vertebrae, the usual number in mammals. Southwest Pacific (Australia), Red Sea, Indian Ocean (east coast of Africa). A third recent Genus, Rhytina (Steller's sea cow), said to be toothless when adult, inhabited the northern Pacific up to the eight- eenth century, since when no observations of its occurrence have been reported. Order 18: CETACEA. Aquatic; many of them of gigantic size (85 feet or more in length) and including the largest known mammals. External form fishlike; no externally evident neck region; seven cer- vical vertebrae much shortened and more or less fused together (Fig. 578). Caudal fin ("tail-flukes") horizontal instead of vertical as in fishes; a single median dorsal fin usually present, but devoid of internal skeleton. Pectoral limb short, broad, externally fmlike, but internally having the skeletal parts of a typical pentadactyl limb; the four or five. Fig. 577. Manatee, Manatus, (Courtesy, American Museum of Natural History, New York.). 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 Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakis
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