882 



D'ARCY WENTWOKTH THOMPSON ON 



from constituting fully two-thirds of the whole length of the skull in Crocodilus, it 

 now constitutes less than half, or, say, three-sevenths of the whole ; and the whole 

 skull, and especially its posterior part, is curiously compact, broad, and squat. The 

 orbit is unusually large. If in the diagram of this skull we select a number of points 

 obviously corresponding to points where our rectangular co-ordinates intersect 

 particular bones or other recognisable features in our typical crocodile, we shall 

 easily discover that the lines joining these points in Notosuchus fall into such 

 a co-ordinate network as that which is represented in fig. 41. To all intents and 

 purposes, then, this not very complex system, representing one harmonious " deforma- 





/"•" 



V\ 



















s 









1 - ■ 









■ 



















i 













Fig. 39. — Crocodilus porosus. 



Fig. 40. — Crocodilus americanus. 



Fig. 41. — Notosuchus lerrestris. 



tion," accounts for all the differences between the two figures, and is sufficient to 

 enable one at any time to reconstruct a detailed drawing, bone for bone, of the skull 

 of Notosuchus from the model furnished by the common crocodile. 



The many diverse forms of Dinosaurian reptiles, all of which manifest a strong 

 family likeness underlying much superficial diversity, furnish us w T ith plentiful 

 material for comparison by the method of transformations. As an instance, I have 

 figured the pelvic bones of Stegosaurus (fig. 42) and of Camptosaurus (fig. 43) to 

 show that, when the former is taken as our Cartesian type, a slight curvature and 

 iin approximately logarithmic extension of the x-axis brings us easily to the con- 

 figuration of the other. In the original specimen of Camptosaurus described by 

 Marsh,* the anterior portion of the iliac bone is missing ; and in Marsh's restoration 

 tins part of the bone is drawn as though it came somewhat abruptly to a sharp point. 



* Dinosaurs of Sorth America, 1896, pi. lxxxi, etc. 



