1888.] ON THE SKELETAL ANATOMY OF THE MESOSUCHIA. 417 



1. Contribution to the Skeletal Anatomy of the Mesosuchia 

 based on Fossil Remains from the Clays near Peter- 

 borough in the Collection of A. Leedsj Esq. By J. W. 

 HULKE, F.Z.S. 



[Eeceived July 14, 1888.] 



(Plates XVIII. & XIX.) 



The primary divisions of the Order Crocodilia laid down by 

 Cuvier (1), and extended by R. Owen (2) and by T. Huxley (3), 

 are so true to nature that they have been substantially adopted by 

 all subsequent writers and have proved insusceptible of material 

 modification. However, within these great divisions the classifi- 

 cation of the Crocodilia has, as Strauch truly remarks with reference 

 to its extant members, ever constituted one of the more difficult 

 tasks of the systematic herpetologist (4). This he rightly attributes 

 principally to the small amount of material available for an exhaustive 

 study of the entire skeleton of the several Crocodihan species 

 preserved in our Museums, and in some measure to the mutable 

 nature of those parts from which the systematic herpetologist has 

 mainly taken the distinctive characters he employs, viz. — the skull, 

 in which the proportions of the proper cranial and the facial region 

 notably alter with the age of the individual in all species ; and the 

 integument, the scutes of which exhibit, within limits, differences as 

 regards their shape and their arrangement in the same species. 

 Even now, after an interval of more than twenty years since the 

 publication of Strauch's admirable synopsis (5), no public osteo- 

 logical collection in this metropolis, so far as I can ascertain, 

 possesses a series illustrating the changes of form which the Croco- 

 dilian skeleton undergoes in its growth from the young to the 

 mature individual in any one species. Indeed as regards one — 

 Gavialis, and this not the least important, I find that neither the 

 British Museum nor that of the Koyal College of Surgeons contains 

 a single entire skeleton. The latter, however, possesses a few 

 detached bones of this genus (crania are well represented in both 

 collections). Exact and comprehensive anatomical knov\ ledge not 

 limited to external features, but extended to the whole skeleton and 

 to the soft parts, must form the only safe basis of any enduring classifi- 

 cation. As regards the extinct members of the Order, the difficulties 

 are for very obvious reasons greatly increased. Highly instructive 

 as are the magnificent skeletons bedded in slabs of rock that adorn our 

 galleries, these often fail to afford information respecting forms and 

 structural details which yet may be of first-rate importance. Ob- 

 viously many such details can only be apprehended by the study of 

 detached bones that can be separately handled, and be viewed in turn 

 from every side. It is the facility for such study that gives a high 

 value to a large collection of Crocodilian remains from pits opened iu 



