Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . ed upon the movements of the tail; andthe largest assemblage of muscles consists of thosewhich give it the lateral flexions that have beenjust described. For this purpose all the impor- 414 THE MECHANICAL FUNCTIONS. tant viscera are placed forwards, and crowdedtowards the head. No room is allowed for aneck ; and the abdomen may be almost regardedas continuous vyith the head, there being properlyno intervening thorax; for the respiratory organsare situated rather beneath than behind thehead.
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . ed upon the movements of the tail; andthe largest assemblage of muscles consists of thosewhich give it the lateral flexions that have beenjust described. For this purpose all the impor- 414 THE MECHANICAL FUNCTIONS. tant viscera are placed forwards, and crowdedtowards the head. No room is allowed for aneck ; and the abdomen may be almost regardedas continuous vyith the head, there being properlyno intervening thorax; for the respiratory organsare situated rather beneath than behind thehead. All this has been done with a view toleave ample scope for the prolonged expansionof the coccygeal vertebrae, and of their muscles,which compose more than half the bulk of theanimal. Having seen how all impediments to the freemotion of the tail have been carefully removed,let us next inquire into the mechanism by whichmobility has been given to that organ. The firstpeculiarity we meet with in the structure ofthe spine of fishes is the mode in which thevertebrae are connected together. The bodies of. each vertebra, as may be seen in Figures 186and 187, are hollowed out, both before and i SKELETON OF FISHES. 415 behind, (considering the spinal column as ex-tended horizontally), so as to form cup-likehollows: by which means, where the concavesurfaces of two adjacent vertebrge are applied toone another, a cavity, having the shape of adouble cone, is formed by the junction of themargins of these conical hollows. These cavi-ties are distinctly seen laid open in Fig. 188,which represents a vertical section of threeadjacent vertebrae of a cod. The edges that arein contact, are united all round by an elasticligament, which readily yields to the bending ofthe vertebrse upon one another by the applica-tion of any force to one side of the spine, andrestores it to its former state when the force hasceased to act. The extent of motion in eachjoint is but small; but being multiplied in thewh
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