Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . he nervoussystem. In laying the foundations of the skeleton,then, the first object is to provide for the secu-rity of the spinal cord : and this is accomplishedby enclosing it within a series of cartilaginousrings, which are destined to shield it during itsgrowth, and by their subsequent ossification, toprotect it most effectually from all injurious pres-sure. It is this part of the skeleton, accordingly,of which the rudiments appear the earliest in theembryo animal. These rings form a colu
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . he nervoussystem. In laying the foundations of the skeleton,then, the first object is to provide for the secu-rity of the spinal cord : and this is accomplishedby enclosing it within a series of cartilaginousrings, which are destined to shield it during itsgrowth, and by their subsequent ossification, toprotect it most effectually from all injurious pres-sure. It is this part of the skeleton, accordingly,of which the rudiments appear the earliest in theembryo animal. These rings form a columnextending in a longitudinal direction along thetrunk ; retracing to us the series of horny rings,in which the bodies of worms, of insects, andindeed of all the Articulata, are encased. Whenossified, these several rings are termed vertehrcB;and the entire column which they compose isthe Spine. Fig. 177 shows the form of one of 388 THE MECHANICAL FUNCTIONS. the vertebrae of the back in the human ske-leton. Fig. 178 is a side view of four vertebraejoined together, and Fig. 179 is a vertical section A. of the same part of the spine, showing the canalformed by the rings. From the constancy withwhich the spinal column is found in all animalsof this type, and from the uniformity of theplan on which, amidst endless variations, it ismodelled, it has been chosen as the distinctivecharacter of this great assemblage of animals,which have accordingly been denominated theVertehrata, or Vertehrated Animals. Nor is the spine of less importance whenviewed in its mechanical relations to the rest ofthe skeleton. It is the great central beam ofthe fabric ; establishing points of union betweenall its parts, and combining them into one con-thiuous frame-work : it is the general axis ofall their motions, the common fulcrum on whichthe principal bones of the extremities are madeto turn : it furnishes fixed points of attachment VERTEBRAL COLUMN. 389 to all the large muscles which act upon thesebones
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