158 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



In Polemarchus gigas, the outer toe curves slightly inwards like 

 the others (Plate 9, fig. 1). In most of the four and five-toed 

 tracks, the curvature is all one way, so as to make the curves of 

 the several toes somewhat concentric ; sometimes towards the line 

 of direction, as in the species of Harpedactylus (Plate 14, figs. 

 2 and 3) ; at other times it is away from the line of direction, as 

 in Atiomcepus Barruttii (Plate 14, fig. 1) and Ancyro'pus heterocli- 

 tus (Plate 15, fig. 3). The curvature of the hind toe is usually so 

 small, that I have not attempted to measure it. 



If a straight line be drawn from the root to the tip of the toe, and 

 another perpendicular to it where the curve is most distant, the 

 length of this last line, measured from the centre of the toe, I call 

 the versed sine, 



I have sometimes suspected that this curvature resulted from 

 the position of the animal's feet in relation to the line of direction ; 

 so that when it made a muscular effort to urge forwards the body, 

 it would throw the toes into a curved position. But upon re- 

 flection, such a movement, it seems to me, would cause the toes 

 to slide so much, that some vestige of the movement would remain, 

 which I have never seen. I rather incline to the opinion, there- 

 fore, that this curvature is the natural state of the foot, and such as 

 we see in many reptiles. 



17. Angle made by the axis of the foot with the line of direc- 

 tion. — By the line of direction, I mean the course taken by the 

 animal as it walked along the surface. To determine this accu- 

 rately, we must have at least three tracks, and if possible four. 

 The axis of the foot is a line drawn from the middle of the heel 

 to the tip of the longest toe. Now in some species of animals, as 

 they walk, these two lines nearly or quite coincide ; as in the 

 Grallae among birds. But in other animals, with short legs, or 



