File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14784609663).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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pass directly from onepoint to another, across the joint; or else they are attachedto cartilaginous plates, which, for the purpose of receivingthe muscles, are made to project intothe interior of the up-per portion of the limb, being themselves immoveably con-nected with the lower portion. By this expedient, not onlyis the employment of a tendon dispensed with, but a largersurface is presented for the attachment of the muscles, whichby acting also upon a longer lever, obtain great mechanicaladvantage. It would be superfluous to occupy more time inexplaining the minutiae of structure in these joints, becausethe simple inspection of the limbs of a crab or lobster willgive clearer ideas of this mechanism than can be conveyedby any laboured description. We must content ourselveswith a brief sketch of the principal constituent parts of theseexternal members of the Crustacea. The number of pairs of legs is either three or four: eachleg is divided into five pieces. The piece ii, (Fig. 137,)
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next the trunk, is termed the haunch, to which is unitedthe trochanter, t; after which comes in succession the fe-mur or thigh, f; two portions of the leg, l; and the tarsusp. The haunch is usually short, being interposed merely asa base for increasing the extent of motion of the pieceswhich follow; and sometimes it is itself composed of more 206 THB MECHANICAL FUNCTIONS. than one piece. The leg is usually divided into two pieces,by a joint. The tarsus is terminated by a single or doublehook, and sometimes by a pincer, or claw. New organs, not met with among the Arachnida, are herefor the first time developed, namely, the Antennse^ of whichthere is one on each side of the head. They are denomi-nated, in popular language, the feelers; although it is morethan probable that they perform some function of higher^importance than that of conveying perceptions of meretouch. The antennae consist of slender filaments, composedof a great number of pieces articulated together: and theyare infinit

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