a new Fossil Animal . 
579 
Bones of the Posterior Extremities . 
Those of the pelvis have not yet been seen in a perfect state ; 
but as Sir E. Home has stated, they closely resemble those of the 
Crocodile. The femoral bone and posterior paddle are altogether 
analogous to the humerus and anterior paddle ; but, contrary to 
the posterior extremities of quadrupeds in general, very considerably 
smaller, nearly in the proportion of one to two ; the reasons of this 
variation are obviously the same which lead to a similar diminution 
of the analogous parts in seals, and their total disappearance in 
cetacea ; namely the necessity of placing the centre of the organs 
producing and regulating motion when acting laterally, before the 
centre of gravity.* 
General Remarks . 
From the dislocated and imperfect state of the skeletons of this 
animal, it is not easy to ascertain the relative proportions of the 
several parts ; but from a careful examination of the most entire, 
it would appear that the head and jaws occupy about one fourth 
of the total length of the animal. 
The size to which the animals of this genus sometimes attained 
may be inferred from a head in the possession of Mr. Johnson of 
Clifton, in which the longest axis of the orbit is 14| inches. 
* This remark applies only to animals moving swiftly through a sensibly resisting 
medium; for the same reason the wings of birds are placed in the fore part of their body; 
and to turn to works of art, the centre of the moving forces given to ships by their sails 
is similarly placed ; were it otherwise, a slight disturbing force near the head of the 
moving body, would instantly swing it round. The great organ of motion in fishes, the 
tail, is indeed posteriorly placed ; but this by its mode of action generates a vis a tergo, 
which can only impel the animal straight forwards; and does not therefore operate under 
the same conditions with organs laterally applied. 
