On the Origin of the Vertebrate Skeleton. 265 



XXVllI.—The Origin of the Vertebrate Skeleton'^. 

 By Harry G. Seeley, St. John's College, Cambridge. 



§ 1. The Problem of Osteology. 



The facts of comparative osteology are the growth of similar 

 constituent bones of skeletons to different extent and in dif- 

 ferent directions in the several groups of vertebrate animals. 

 Hence to the palaeontologist the discovery of new types of life 

 in the strata usually means a new and limited growth of a few 

 elements of, the skeleton in definite directions. These pecu- 

 liarities of growth give the skeletons which they characterize 

 a plan of structure which differs from that of other animals ; 

 and therefore that plan becomes comparable with the plans of 

 growth which distinguish the several known groups. The 

 multitudinous array of species is so reduced to a few factors ; 

 and these limiting facts enable the student to investigate and 

 discover the relation of one animal to the remainder, and of 

 all animals to each other, in a manner not dissimilar and 

 with similar success to the way by which meridians of longi- 

 tude and parallels of latitude localize geographical districts. 

 The biological problem admits of infinite complication, from 

 the skeleton being composed of many different bones, each of 

 which has its definite form, which may vary a little in every 

 species of the group. And though a few general plans may 

 accurately be spoken of as limiting and comprising this vast 

 difference of detail, yet there is no plan except that which is 

 manifested in each and all of the individuals forming the species 

 which the group includes. And if it be necessary, as it is, to 

 see how closely one plan of structm-e approximates to other 

 plans, or how it differs from them, such a result can only be 

 attained by comparing and contrasting individuals which 

 manifest the kind of growth which is named the plan of the 

 group. 



Here comparative osteology offers for investigation the 

 subject of growth of bone. And if a sufficient elucidation of 

 that question can be given, less difficulty will be experienced 

 in understanding the nature of the special growths in specified 

 directions which give a common plan to each of the several 

 zoological groups of Vertebrata named orders. 



The skeleton, however, is but a degraded portion of the 

 organism ; and, in the kinds of animals which inhabit the world 

 now, the fimctions of the several bones are often known, as 

 well as the nature and modifications of the soft stractures. 



nerves, vessels, viscera, muscles, which are correlated with 



* Being an introductory chapter from the Author's MS, ' Osteology of 

 the Eeptilia.' 



Ann. & Mag. N. Hist. Ser.4. Fb?. ix. 19 



