. Animal biology. Biology; Zoology; Physiology. 322 ANIMAL BIOLOGY. chief limb bones themselves are lengthened, subsidiary ones are suppressed, and the wrist and ankle are raised still further from the ground, so that merely the tips of one or two digits of each limb support the animal (unguli- grade). Thus the typical cur- sorial forms represent the culmi- nation of Mammalian adaptation to plains and steppes; regions in which long distances must fre- quently be traversed in quest of food, and safety is to the swift. (Fig. 203.) Another line of adaptive radia- tion is presented by the tree dwe
. Animal biology. Biology; Zoology; Physiology. 322 ANIMAL BIOLOGY. chief limb bones themselves are lengthened, subsidiary ones are suppressed, and the wrist and ankle are raised still further from the ground, so that merely the tips of one or two digits of each limb support the animal (unguli- grade). Thus the typical cur- sorial forms represent the culmi- nation of Mammalian adaptation to plains and steppes; regions in which long distances must fre- quently be traversed in quest of food, and safety is to the swift. (Fig. 203.) Another line of adaptive radia- tion is presented by the tree dwellers: arboreal forms which make their own the world of foliage high above the ground. Such are, for instance, the Sloths which are really tree climbers that walk and sleep upside down suspended from branches; the tailless Apes that swing among the boughs chiefly by their arms; and the Squirrels that scamper along the branches. Some Squir- rels and the so-called Flying Le- murs take long soaring leaps sup- ported by wide folds of skin between the sides of the body and the extended limbs. But the Mammals have not left the air untenanted, for truly volant forms are represented by the Bats in which the fore limbs with greatly elongated fingers form the framework of true wings. (Figs. 204, 207.) Passing below the surface of the mals. A plantigrade; B, digitigrade; earth FOSSQRIAL Mammals are C, unguhgrade. (*rom Lull, alter. 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 Woodruff, Lorande Loss, 1879-1947. New York The Macmillan company
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