File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14764435552).jpg

Identifier: animalvegetable01roge (find matches)
Title: Animal and vegetable physiology, considered with reference to natural theology
Year: 1836 (1830s)
Authors: Roget, Peter Mark, 1779-1869
Subjects: Biology Physiology Plant physiology Natural theology
Publisher: Philadelphia, Carey, Lea & Blanchard
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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is enemies to dislodge or annoy him. These considerations supply us with a key to many ofthose apparent anomalies, which cannot fail to strike us inviewing the dispositions of the parts of the skeleton (Fig.213,) and the remarkable inversion they appear to have un-dergone, when compared with the usual arrangement. Wefind, however, on a more attentive examination, that all thebones composing the skeleton in other vertebrated animalsexist also in the tortoise; and that the bony case which en-velops all the other parts is really formed by an extension Vol. I. 41 322 THE MECHANICAL FUNCTIONS. of the spinous processes of the vertebrae and ribs on the oneside, and of the usual pieces which compose the sternum onthe other. The upper and lower plates thus formed areunited at their edges by expansions of the sternocostal ap-pendices, which become ossified. Thys, no new elementhas been created; but advantage has been taken of those al-ready existing in the general type of the vertebrata, to mo-
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dify their forms, by giving them different degrees of rela-tive development, and converting them, by these trans-formations, into a mechanism of a very different kind, andsubservient to other objects than those to which they areusually applied. It is scarcely possible to have strongerproofs, if such were wanting, of the unity of plan which hasregulated the formation of all animal structures, than thoseafforded by the skeleton of the tortoise. The first step taken to secure the relative immobility ofthe trunk, is to unite in one rigid bony column all its verte- CIIELONIAN REPTILES. 323 brae, and to allow of motion only in those of the neck, andof the tail. The former, accordini»;ly, are all anchylosed to-gether, leaving, indeed, traces of their original forms as se-parate vertebrae, but exhibiting no sutures at the place ofjunction. The canal for the spinal marrow is preserved, asusual, above tlic bodies of these coalesced vertcbric, and isformed by their united leaves; the arches bei

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