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FIG. 312.

1

Skeleton of the Tortoise (plastron removed): a, cervical vertebræ; c, dorsal vertebræ; d, ribs; e, marginal bones of the carapace; 7, scapula; k, precoracoid; b, coracoid; f, pelvis; i, femur; g, tibia; h, fibula.

Skeleton of a Vulture: 1, cranium

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FIG. 313.the parts of which are separable only in the chick; 2, cervical vertebræ; 3, dorsal; 4, coccygeal, or caudal; the lumbar and sacral are consolidated; 5, ribs; 6, sternum, or breastbone, extraordinarily developed; 7, furculum, clavicle, or "wishbone"; 8, coracoid; 9, scapula; 10, humerus; II, ulna, with rudimentary radius; 12, metacarpals; 13, phalanges of the great digit of the wing; 19, thumb; 14, pelvis; 15, femur; 16, tibiatarsus and fibula, or crus; 17, tarsometatarsus; 18, internal digit, or toe, formed of three phalanges; the middle toe has four phalanges; the outer, five; and the back toe, or thumb, two.

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FIG. 314.

Skeleton of the Horse (Equus caballus): 22, premaxillary; 12, foramen in the maxillary; 15, nasal; 9, orbit; 19, coronoid process of lower jaw; 17, surface of implantation for the masseter muscle; there are seven cervical vertebræ, nineteen dorsal, D-D; five lumbar, a-é; five sacral, f-l; and seventeen caudal, p-r; 51, scapula, or shoulder blade; i, spine, or crest; h, coracoid process (acromion wanting); 1, first pair of ribs (clavicle wanting, as in all Ungulates); e, sternum; a, shaft of humerus; b, deltoid ridge; g, head fitting in the glenoid cavity of the scapula -near it is a great tuberosity for the attachment of a powerful muscle; k, condyles; 54, radius, to which is firmly anchylosed a rudimentary ulna, 55, the olecranon; 56, the seven bones of the carpus, or wrist; 57, large metacarpal, or cannon bone," with two "splint bones"; 58, fetlock joint; 59, phalanges of the developed digit, corresponding to the third finger in man; 62, pelvis; 63, the great trochanter, or prominence on the femur, 65; 66, tibia; 67, rudimentary fibula; 68, hock, or heel, falsely called knee; 69, metatarsals.

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CHAPTER XX*

HOW ANIMALS MOVE

1. The power of animal motion is vested in protoplasm, cilia, and muscles. The power of contractility is one of the fundamental physiological properties of protoplasm, like sensibility and the power of assimilation. Protoplasmic animals, like the amoeba and Rhizopoda (Figs. 1, 213), move by the contractility of their protoplasm, as also may the embryos of higher animals upon the yolk of the egg. Protoplasm may be extended into projections called pseudopodia, by whose contraction the animal may move.

Infusoria, and nearly all higher animals, possess cilia (Figs. 9, 11). These are short microscopic threads of protoplasm which have the power of bending into a sickle shape and straightening out. As they bend much faster than they straighten, and as they all work together, they can cause motion of the animal, or may serve to produce currents in the water, the animal remaining at rest. They are seen on the outside of Infusoria, and of embryos of very many higher animals, serving as paddles for locomotion; they line the channels in the gills of the oyster, creating currents for respiration; and they cover the walls of the passages to our lungs to expel the mucus. Flagella (Figs. 4, 5, 6) are a sort of long cilia, which are thrown into several curves when active, resembling a whiplash, whence their name. Both cilia and flagella seem to be wanting in arthropods.

* See Appendix.

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