OP THK OSSEOUS SYSTEM. 357 



the hard parts of the other articulated animals, and especially 

 those of the insecta and Crustacea, ought to have been assimi- 

 lated to the bones, for it is in the latter that voluntary motion 

 and the preservation of the form of the body are carried to the 

 highest pitch. Willis, in speaking of the crab, uses the fol- 

 lowing words: Quo ad membra etpartes matrices, non ossa 

 teguntur carnibus, sed carries ossibus. 



Aristotle, however, who already considered the spine as the 

 origin, or centre, from which the bones are derived, had giv- 

 en the first intimation respecting the distinction which has in 

 these latter times been made between the bones and the other 

 hard parts of animals. According to this idea, the skeleton, 

 or osseous system of the vertebrate animals is, in fact, first, 

 and principally seen to consist of a longitudinal column, which 

 furnishes superiorly, or posteriorly, an envelope to the spinal 

 marrow and brain, and anteriorly, or inferiorly, another en- 

 velope to the organs of nutrition, and especially to the central 

 parts of the vascular system. Other less constant appendages 

 are subservient to motion through their articulations. All the 

 parts of the system, besides, may furnish attachment to mus- 

 cles. 



The question, therefore, is, whether all the hard and dry 

 parts of the body of animals, those which determine its form 

 and facilitate its motions, are to be called bones and skeleton; 

 or if these names are to be restricted to the hard parts, pecu- 

 liar to the vertebrate animals, which form a central and median 

 column in the body, with a cavity for the nervous trunk, and 

 another cavity for the heart and aorta, and frequently lateral 

 appendages for motion. 



According to M. GeoffYoi Saint-Hilaire, one of the natural- 

 ists who has engaged most deeply in the study of this point 

 of zootomy, and who has treated it with his original talent, 

 there is no doubt on the subject, and all the difference between 

 the skeleton of an articulate and a vertebrate animal, between 

 the rachis of a crustaceous animal or an insect, and that of an 

 osseous animal, depends upon the absence of a spinal marrow 

 in the former, and its presence in the latter; a difference which 

 renders necessary a rachis with two canals in the vertebrate 



