File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14778718512).jpg

Identifier: animalandvegetab01roge (find matches)
Title: Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget ..
Year: 1834 (1830s)
Authors: Roget, Peter Mark, 1779-1869
Subjects: Biology Physiology Plant physiology Natural theology
Publisher: London : W. Pickering
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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forts of his enemies to dislodge or annoy him. These considerations supply us with a key tomany of those apparent anomalies, which cannotfail to strike us in viewing the dispositions-ofthe parts of the skeleton (Fig. 213), and the re-markable inversion they appear to have under-gone, when compared with the usual arrange-ment. We find, however, on a more attentiveexamination, that all the bones composing theskeleton in other vertebrated animals exist alsoin the tortoise; and that the bony case whichenvelopes all the other parts is really formed byan extension of the spinous processes of the ver-tebrae and ribs on the one side, and of the usualpieces which compose the sternum on the other.The upper and lower plates thus formed areunited at their edges by expansions of the sterno- CHELONIAN REPTILES. 465 costal appendices, which become ossified. Thusno new element has been created; but advantagehas been taken of those already existing in thegeneral type of the vertebrata, to modify their
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forms, by giving them different degrees of relativedevelopement, and converting them, by thesetransformations, into a mechanism of a very dif-ferent kind, and subservient to other objectsthan those to which they are usually applied.It is scarcely possible to have stronger proofs, ifsuch were wanting, of the unity of plan whichhas regulated the formation of all animal striic- VOL. I. H H 466 THE MECHANICAL FUNCTIONS. tures, than those afforded by the skeleton of thetortoise. The first step taken to secure the relativeimmobility of the trunk, is to unite in one rigidbony column all its vertebrae, and to allow ofmotion only in those of the neck, and of the tail.The former, accordingly, are all anchylosed to-gether, leaving, indeed, traces of their originalforms as separate vertebrae, but exhibiting nosutures at the place of junction. The canal forthe spinal marrow is preserved, as usual, abovethe bodies of these coalesced vertebrae, and isformed by their united leaves ; the arches beingc

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