Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . of a still greaternumber. In the rattle-snake (Crotaliis horridus)there are about two hundred ; and above threehundred have been counted in the spine of theColuber natrix. These vertebrae are all united by ball and socket joints,as in the adult batrachia;the posterior rounded emi-nence of each vertebrabeing received into theanterior surface of thenext. Fig. 202 is a viewof this portion of the ske-leton in the Boa con-strictor, showing the arti-culation of the ribs withthe pr
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . of a still greaternumber. In the rattle-snake (Crotaliis horridus)there are about two hundred ; and above threehundred have been counted in the spine of theColuber natrix. These vertebrae are all united by ball and socket joints,as in the adult batrachia;the posterior rounded emi-nence of each vertebrabeing received into theanterior surface of thenext. Fig. 202 is a viewof this portion of the ske-leton in the Boa con-strictor, showing the arti-culation of the ribs withthe provision has thus been made for extentof motion, extraordinary care has at the sametime been bestowed upon the security of thejoints. Thus we find them effectually protectedfrom dislocation by the locking in, above andbelow, of the articular processes, and by theclose investment of the capsular ligaments. Thedirection of the surfaces of these processes, andthe shape and length of the spinous processes,are such as to allow of free lateral flexion, but tolimit the vertical and longitudinal motions: and. SERPENTS. 451 whatever degree of freedom of motion may existbetween the adjoining vertebrae, that motionbeing multiplied along the column, the flexibilityof the whole becomes very great, and admits ofits assuming every degree and variety of curva-ture. The presence of a sternum, restrainingthe motions of the ribs, w ould have impeded allthese movements, and would have also been aninsurmountable bar to the dilatation of the sto-mach, which is rendered necessary by the habitof the serpent of gorging its prey entire. The mode in which the boa exerts a powerfulpressure on the bodies of the animals it hasseized, and which it has encircled within itsfolds, required the ribs to be moveable laterally,as well as backwards, in order to elude the forcethus exerted. The broad convex surfaces onwhich they play give them, in this respect, anadvantage which the ordinary mode of articula-tion woul
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