The principal forms of the skeleton and the teeth : as the basis for a system of natural history and comparative anatomy / by Professor Owen.

  • Owen, Richard, Sir, 1804-1892.
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: The principal forms of the skeleton and the teeth : as the basis for a system of natural history and comparative anatomy / by Professor Owen. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    jaws are singularly bent down, and the upper jaw is armed with a pair of short tusks. The bones of all these cetacea are singularly massive and compact. Three or four of the anterior thoracic ribs are joined to a sternum—the rest are free. One of the vertebras intervening between the costal and caudal series has connected with it a simple pelvic arch, in which the ilium and ischium may be recognised, and a still more rudimental condition of such arch is suspended in the inguinal muscles of the true cetacea. Most of the caudal vertebras (Fig. 26), cd, of the manatee and dugong, have long diapophyses, and haemal arches (Fig. 26), h. The terminal vertebras are flattened horizontally. The lacteal organs of the dugong are placed on the breast, and the pectoral fins, in the female at least, are applied to clasp the young ; and the animal so observed, with its own head, and that of its young above water, has given rise to the fable of the siren and mermaid. The bones and joints of the pectoral fin are accordingly better developed than in the ordinary whales. The first row of carpal bones, 56, consists of two—one articulated to the radius, 55, the other to the ulna, 54, and fifth digit, 57, v, and both to the single bone representing the second row. The first digit, i, consists of a short metacarpal; the metacarpals of the others support each three phalanges. Skeleton of the Seal.—In the seal tribe (Phociclce) another and well-marked stage is gained in the development of the terrestrial instruments of locomotion. Hind limbs are now added — the marine mammal has become a quadruped. The sphere of life of the seals is near the shores ; they often come on land; they sleep and bring forth among the rocks and littoral caves : hence the necessity for a better development of the pectoral limbs, although these, like the pelvic ones, still retain the general form of fins. The fish-hunting seals make more use of the head in independent movements of sudden Fig. 27. r skeleton of the walrus (Trichecus rosmarus). extension, retraction and quick turns to the right and left, than do the cetacea of like diet; and the walrus (Fig. 27) works the head, as the place of attachment of its long, vertical, down-growing tusks, in various movements required in clambering over floes and bergs of ice. Accordingly, in the seal tribe we find the seven neck vertebras (ib.) c, longer, and with more finished and free-playing joints than in the whales and dugongs. The sigmoid curve, in which they can be thrown during retraction of the head, exceeds