LITHORNIS VULTURINUS. 553 



Sacrum of a Bird, eocene clay, Sheppey. Nat. size. 



Figures 233, A and B, give two views of the second 

 ornitholite from Sheppey, alluded to in the preceding 

 section : in the side-view, A, ten vertebrae are anchylosed 

 together, and the under view, B, shows the complete con- 

 fluence of the vertebral bodies. The long sacrum thus 

 formed is peculiar to birds, and relates to the unfavour- 

 able position of a horizontally disposed trunk for support 

 on a single pair of limbs, compensation being made by 

 the great extent of the axis of the trunk, which is grasped, 

 as it were, by the iliac bones, and the weight transferred 

 by these to the heads of the obliquely-placed thigh-bones. 

 As all birds, whether they have the power of flight or not, 

 are bipeds and prone, the long sacrum is common to all, 

 and its structure does not present such well-marked modi- 

 fications as to permit any satisfactory deductions from the 

 present mutilated specimen of the precise position in the 

 feathered class of the ancient bird which it represents. 



The specimen itself forms part of the choice collection 

 of J. S. Bowerbank, Esq., F.R.S. 



