THE SHAPES OP VERTEBRATE SKELETONS. 225 



[NOTE. The theory set forth in the foregoing chapter, is 

 an elaboration of one suggested at the close of a criticism 

 of Prof. Owen's Archetype and Homologies of the Vertebrate 

 Skeleton, already referred to in 210 as having been pub- 

 lished in the Medico-Chirurgical Review for October, 1858. 

 It is now reproduced in Appendix B. Since the issue of this 

 elaborated exposition, in No. 15 of my serial in December, 

 1865, verifications of it have from time to time been published. 

 In his work The Primary Factors of Organic Evolution, 

 Prof. Cope of Philadelphia writes : 



" Mr. Herbert Spencer has endeavoured to account for the 

 origin of the segmentation of muscles into myotomes, and 

 the division of the sheath of the notochord into vertebrae, 

 by supposing it to be due to the lateral swimming movements 

 of the fishes, which first exhibit these structures. With this 

 view various later authors have agreed, and I have offered 

 some additional evidence of the soundness of this position 

 with respect to the vertebral axis of Batrachia, and the 

 origin of limb articulations. It is true that the origin of 

 segmentation in the vertebral column of the true fishes and 

 the Batrachia turns out to have been less simple in its pro- 

 cess than was suggested by Mr. Spencer, but his general 

 principle holds good, now that paleontology has cleared up 

 the subject" (pp. 367-8). 



An allusion in the foregoing extract is made by Prof. Cope 

 to certain observations set forth in his work entitled The 

 Origin of the Fittest. On pp. 305-6 of it will be found the 

 following sentences : 



" Now, all the Permian land-animals, reptiles and batra- 

 chians, retain this notochord with the elements of osseous 

 vertebrae, in a greater or less degree of completeness. There 

 are some in South Africa, I believe, in which the ossification 

 has come clear through the notochord; but they are few. 

 . . . There is something to be said as to the condition of 

 the column from a mechanical standpoint, and it is this: 

 that the chorda exists, with its osseous elements disposed 

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