1889.] '*^'^ [Ryder. 



" A C'riticum on Prof. Owen's Theory of the Vertebrate Skeleton," and pub- 

 lished in [he BritisJi and Foreign Medico-C'hirurgkal Review for October, 

 1858. I find that it is possible on the basis of fact to completely substan- 

 tiate, so far as the vertebral column is concerned. Mr. Spencer's conclu- 

 sion, stated near the close of the article just cited, that : " It is a perfectly 

 tenable supposition that all higher vertebrate forms have arisen by the 

 superposing of adaptations upon adaptations." 



I find in fact that not only have the successively higher and higher 

 types of vertebral elements grown out of one another in succession as the 

 consequence of superimposition of new characters, but also that as a result 

 of such superimpositions of new features a complex series of substitutions 

 have resulted, which it is not in place to discuss in detail in this connec- 

 tion. It may be demonstrated that the growth and evolution of the 

 jointed calcified vertebral column, after the development of the notochord 

 was achieved and upon which the first expression of a segmented support 

 was moulded, could take place in only one way, in forms with a free 

 larval stage or such as developed quickly into an active organism, followed 

 by a prolonged period of growth. It may also be proved that the only 

 jointed calcified structure which could here satisfy the requirements of 

 rapid, tridimensional, continuous growth in such a case without entailing 

 inefficiency was the biconcave type of vertebrae, which are thus found to 

 have a profound physiological and adaptive significance which has never 

 hitherto been even dreamt of by the ordinary '= Ding an Sick" school of 

 morphologists, the offspring of the one-sided training now practiced in all 

 European and American biological laboratories, in which the microscope, 

 microtome and homologies, real or fancied, are the reigning fetishes. It 

 may be shown also that the development of the vertebral bodies under 

 such conditions is exogenous ; that the mechanical conditions, definite 

 motions and space relations of the parts involved are the determining 

 factors in the evolution of a definitely-shaped succession of segments 

 moulded upon a preexisting notochordal rod. It may also be shown that, 

 as layer after layer of new matter is superimposed upon the first trace of 

 a vertebral body, these layers become successively wider and Avider, and 

 that the last formed or youngest and most external layers are the onlj'^ 

 ones which articulate by their edges and form the points of contact of the 

 ends of the cylindrical vertebral bodies. It is thus easy to understand 

 that, with every increment of growth, a new articulation is established 

 between every two successive vertebrae, and that at the same time the 

 innermost and first annular rings of calcified vertebral substance of suc- 

 cessive vertebraj are pushed as much farther apart as the new rings at the 

 periphery have grown in additional width. Thus arises that marvelously 

 ingenious yet extremely simple form of calcified vertebral body which not 

 only furnishes the means of continuous growth, but also that of continuous 

 functional activity. 



It may also be rendered certain that it is such a biconcave form of 

 vertebral body which forms the basis out of which all the others have 



