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  Section: Anatomy of Vertebrate Animals » Organisation of the Vertebrata Skeleton
 
 
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Organisation of the Vertebrata Skeleton

 
     
 
The Vertebrata are distinguished from all other animals by the circumetance that a transverse and vertical section of the body exhibits two cavities, completely separated from one another by a partition. The dorsal cavity contains the cerebro-spinal nervous system; the ventral, the alimentary canal, the heart, and, usually, a double chain of ganglia, which passes under the name of the "sympathetic." It is probable that this sympathetic nervous system represents, wholly or partially, the principal nervous system of the Annulosa and Mollusca. And, in any case, the central parts of the cerebro-spinal nervous system, viz., the brain and the spinal cord, would appear to be unrepresented among invertebrated animals. For these structures are the results of the metamorphosis of a part of the primitive epidermic covering of the germ, and only acquire their ultimate position, in the interior of the dorsal tube, by the development and union of outgrowths of the blastoderm, which are not formed in the Invertebrata. (It is possible that an exception to this rule may be found in the Ascid- ans. The tails of the larva of these animals exhibit an axial structure, which has a certain resemblance to a vertebrate notochord; and the walla of the pharynx arc perforated, much as in Amphioxus.)
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