xviij THE COMPARISON OF RELATED FORMS 753 



or longirostrine, crocodiles, such as the genus Tomistoma ; and, 

 in the species figured, the oblique position of the orbits, the arched 

 contour of the occipital border, and certain other characters suggest 

 a certain amount of curvature, such as I have represented in the 

 diagram (Fig. 383, b), on the part of the horizontal co-ordinates. 

 In the still more elongated skull of such a form as the Indian 

 Gavial, the whole skull has undergone a great longitudinal 

 extension, or, in other words, the ratio of x/y is greatly diminished ; 

 and this extension is not uniform, but is at a maximum in the 

 region of the nasal and maxillary bones. This especially elongated 

 region is at the same time narrowed in an exceptional degree, and 



ABC 

 Fig. 383. A, Crocodilus poro.vis. B, C aniericanus. C, Notosuckus terrestris. 



its excessive narrowing is represented by a curvature, convex 

 towards the median axis, on the part of the vertical ordinates. 

 Let us take as a last illustration one of the Mesozoic crocodiles, 

 the little Notosuckus, from the Cretaceous formation. This little 

 crocodile is very different from our type in the proportions of its 

 skull. The region of the snout, in front of and including the frontal 

 bones, is greatly shortened ; 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 



T. G. 48 



