. The chordates. Chordata. 740 Comparative Morphology of Chordates number of digits. The digits bear claws, in some cases so blunt as to resemble small hoofs. Examples: Mouse, rat (Mus); squirrel (Sciurus—dental for- mula, i 10 2 3\ j, Ct, py, m ~ 1, gopher, woodchuck, beaver (Castor), guinea pig (Cavia), chinchilla, porcupine whose spines resemble those of the hedgehog (an insectivore). The largest living rodent is the South American capybara, semiaquatic, about 4 feet long, resembling a gigantic guinea pig: (Figs. 546, 549, 550).. Fig. 548. Skull of the porcupine, (v) Antorbital vacuity; (11
. The chordates. Chordata. 740 Comparative Morphology of Chordates number of digits. The digits bear claws, in some cases so blunt as to resemble small hoofs. Examples: Mouse, rat (Mus); squirrel (Sciurus—dental for- mula, i 10 2 3\ j, Ct, py, m ~ 1, gopher, woodchuck, beaver (Castor), guinea pig (Cavia), chinchilla, porcupine whose spines resemble those of the hedgehog (an insectivore). The largest living rodent is the South American capybara, semiaquatic, about 4 feet long, resembling a gigantic guinea pig: (Figs. 546, 549, 550).. Fig. 548. Skull of the porcupine, (v) Antorbital vacuity; (11) frontal; (22) premaxillary. Notice the relatively great size of the premaxillaries, which carry the incisor teeth. (Courtesy, Owen: "Comparative Anatomy and Physiology of Vertebrates," London, Longmans, Green & Co., Ltd.) The Order Rodentia includes more living species than any other mammalian order, some estimates of the number approaching 3000. Mostly terrestrial, some are burrowing, some arboreal, a few are aquatic or semiaquatic, and "flying squirrels" sail by spreading out a pair of broad folds of skin extending between fore- and hindlegs. Distribution: World-wide; especially numerous in South America, relatively few in Australia and Madagascar. Rabbits are now abundant in Australia but are not native there, having been introduced by man. Order 8: LAGOMORPHA. Two pairs of upper incisors, those of the more lateral pair being very small; one pair of lower incisors. Tail .203 3 vestigial. Dental formula for rabbit, i y, c t, p ^, m ~ This Order in- cludes only the rabbit, hare, and pika (Fig. 551). Older classifications usually include the lagomorphs as a Suborder. 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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