File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14776689674).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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pellucidity of the mass, and the readi-ness with which the osseous fibres it containscan be distinguished. Another consequence ofthe want of density in the bones of fishes is, that FISHES. 411 their articulations are less regular and perfectthan the corresponding joints of terrestrial ani-mals ; for it is evident that where the parts aresoft and flexible, joints are not required. In the osseous fishes, the bony structures aremore finished ; and they even arrive at a degreeof hardness equal to that of the higher classes.But this developement is not uniform in all thebones; in the head of the pike, for instance,while some of the bones have acquired a greathardness, others remain wholly and permanentlyin a cartilaginous condition. The bones of fishes,however advanced in their ossification, neverreach that stage of the process in which cavitiesare formed ; thus there is no space for marrow,nor even for the cellular or cancellated structurewhich we have noticed in the more perfect bones.*
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The general disposition of the bones which com-pose the entire skeleton will be understood fromFig. 184, which represents that of the Cyprums * Cuvier, sur les Poissous. Tom. i. p. 218. 41*2 THE MECHANICAL FUNCTIONS. carpio, or carp. The muscular flesh of fishes islikewise softer than that of the higher classes;and the cellular substance more attenuated andmore gelatinous ; so that the membranes whichit forms are of a looser and more pulpy texture.Progressive motion in fishes is efi*ected by thesimplest means, the principal instrument em-ployed for this purpose being the tail; for thefins, as we shall presently find, are merely auxi-liary organs, serving chiefly to balance the bodywhile it receives its propulsion from the tail. Afish moves in the water upon the same principleas a boat is impelled in sculling; for the actionof the tail upon the water is lateral, like thatof an oar, which it resembles in the verticalposition of its plane ; and the effect is transferredB by the resistanc

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