Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . quisite that the limbs shouldbe so disposed that the centre of gravity may fall within thespace included by the feet. If the centre of gravity be with- THE MODES OF PKOGRESSION. 153 out these limits, the animal falls to that side towards whichthe centre of gravity inclines. On this account, the albatros,and some other aquatic birds which have their feet placed veryfar back, cannot use them for walking. § 291. The more numerous and the mor
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . quisite that the limbs shouldbe so disposed that the centre of gravity may fall within thespace included by the feet. If the centre of gravity be with- THE MODES OF PKOGRESSION. 153 out these limits, the animal falls to that side towards whichthe centre of gravity inclines. On this account, the albatros,and some other aquatic birds which have their feet placed veryfar back, cannot use them for walking. § 291. The more numerous and the more widely separatedthe points of support are, the firmer an animal stands. Onthis account, quadrupeds are less liable to lose their balancethan birds. If an animal has four legs it is not necessarythat they should have a broad base. Thus we see that mostquadrupeds have slender legs touching the ground by only asmall surface (fig. 169). Broad feet would interfere witheach other, and only increase the weight of the limbs, withoutadding to their stability. Birds are furnished with long toes,which as they spread out, subserve the purpose of tripods. •PS. Fig. 169.—The Skeleton of the Camel. v 0, cervical vertebrae ; v d, dorsal vertebrae ; v I, hrnbar vertebras ; v s,the sacrum; v g, caudal vertebrae; c, the ribs; o, scapula ; h, the humerus;c a, the carpus ; m c, the metacarpus; p h, the phalanges; cu, the radiusand ulna; / e, the femur; r o, the patella; t i, the tioia ; t a, the tarsus :m t, the metatarsus. 154 THE MODES OF PROGRESSION. Moreover, tlie muscles of the toes are so disposed that theweight of the bird causes them to contract firmly, hence birdsare enabled to sleep standing, in perfect security, upon theirperch, and without effort. § 292. In quadrupeds, the joints at the junction of the limbswith the body bend freely in one direction only, that is, to-wards the centre of gravity ; so that if one limb yields, thetendency to fall is counteracted by the resistance o
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
