On a New Species of Scymnognathus (S. tigriceps). 35 



short and broad. The ungual phalanx is long and powerful, but not 

 greatly curved. It manifestly had a powerful claw. 



The 3rd digit has the 1st phalanx short and powerful, almost as 

 broad as long. The 2nd phalanx is very short, its length being only 

 about i of its width. Though so very short it manifestly has 

 hinged freely on both the 1st phalanx and the 3rd. The 3rd 

 phalanx is a strong short bone about as long as broad. The ungual 

 phalanx is like that of the 2nd toe, long and powerful, and only 

 slightly curved. 



The 4th digit has the 1st phalanx short and powerful, very little 

 longer than broad. Following it are two short plate-like phalanges 

 agreeing closely with the short phalanx in the 3rd toe. Each is 

 only about ^ as long as broad, and each seems to have very free 

 movement. The 4th phalanx is much like the penultimate 

 phalanges of the other toes. The ungual phalanx is also similar 

 to that of the 2nd and 3rd toes. 



The 5th digit has only three phalanges the 1st and 3rd like the 

 proximal and distal phalanges of the other toes, and the middle 

 phalanx like the penultimate phalanges of the others. 



It will thus be seen that though the digital formula is 2, 3, 4, 5, 3, 

 the 3rd and 4th toes have been shortened by the 2nd phalanx in the 

 3rd toe, and the 2nd and 3rd phalanges in the 4th toe becoming 

 very much reduced in size. 



Considering the width of the foot the toes are short. The extent 

 of movement of the bones is not quite clear. Probably the animal 

 walked with the foot mostly on the ground after the manner of the 

 bear. Considerable movement seems to have been possible between 

 the carpals and metacarpals, and more between the metacarpals 

 and phalanges. Considerable flexion of the claws on the palm was 

 possible, but the whole hand can only be regarded as a very imper- 

 fect instrument of prehension. 



As it is pretty certain that both the Anornodonts and the Cyno- 

 donts are descended from a Therocephalian ancestor, it would be 

 very interesting to find out exactly how the 2, 3, 3, 3, 3 digital formula 

 was derived from the 2, 3, 4, 5, 3 formula of the Therocephalian. We 

 see clearly one stage the great reduction in length of the 2nd 

 phalanx of the 3rd toe and of the 2nd and 3rd phalanges of the 4th 

 toe, but at present we have no evidence as to whether these reduced 

 phalanges became further steadily reduced or suddenly disappeared. 

 The latter seems the more probable alternative. 



