File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14779051255).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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their full developement. In order toobtain a standard of comparison by which toestimate all their gradations of evolution, it willbe best to consider them first in their moreperfectly developed forms, as they are pre-sented in the higher classes of quadrupeds.In the following descriptions, the skeleton of theHog (Fig. 181) will be taken for the purpose ofreference. The ribs consist of arches of bone affixed attheir upper ends to the bodies of the vertebrae,and also, by a separate articulation, to theirtransverse processes; where, in general, theyare allowed a slight degree of motion. Theirprimary use is to defend the vital organs si-tuated in the region of the chest, or thorax(namely, the heart and the lungs); but theyare subservient also to the function of respira-tion, by the alternate movements that are givento them by their muscles. The two parts, of VOL. I. D D 402 THE MECHANICAL FUNCTIONS. which they are composed, often form an angleby their junction, and at this angle a process
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occasionally extends, for the purpose of formingconnexions with the neighbouring ribs. The ribs are connected in front with thebreast bone, or sternum (s), often by the inter-vention of cartilages, which, from their simi-larity of form to the ribs, appear as continuationsof them, and are provided apparently to eke outthe remainder of the semicircle. These carti-lages, which have been termed the stenio-costalappendices, often become ossified, either whollyor in part. The sternum is formed of nine elementarypieces, each proceeding from a separate centreof ossification. Two of these occupy the endwhich is nearest to the head, four are lateral,and two are situated at the opposite extremity: SKELETON OF VERTEBRATA. 403 one only being central and surrounded by therest. Few subjects in comparative osteology aremore curious and instructive than to trace thedevelopement of these several elementary partsin the different classes of animals, from the ru-dimental states of this bone as it occurs i

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