A NEW HORNED RODENT— GIDLEY. 633 



The hind limbs are lighter and more delicately proportioned than 

 the fore limbs. The femur is nearl}^ straight, with a rather slender 

 shaft, but with well-developed trochanters and broadly expanded con- 

 dyles. The greater trochanter extends somewhat above the head of 

 the fenuir and is confluent with the greatly expanded third trochanter. 

 The condjdes are presented well backward. The surface for the patella 

 is also unusually l)road. 



The tibia is comparatively short, not equaling the femur in length, 

 and is remarkably modified. The cnemial crest is greatly expanded 

 and extends well down the shaft, converting the proximal two-thirds 

 into a thin expanded sheet of bone, deeply concave on the outer or 

 flbular side and convex on the inner face. The entire shaft is greatly 

 twisted laterally, as shown in Plate LXII, tig. <% the distal end being 

 turned to such a degree as to carry the fibular facet to a position nearl}^ 

 in front, with the median ridge of the tibio-tarsal facet placed nearly 

 at a right angle to the fore and aft plane of the tibia. This arrange- 

 ment throws the foot inward at a great angle, with its outer side pre- 

 sented nearly forward when the tibia and femur are placed in the 

 usual normal position. In Mylagaulus the tibia is apparently less 

 modified. 



The fil)ula is entirely free but much reduced. A considerable extent 

 of the distal end of the shaft comes in contact with the tibia, as in 

 Apladoiitfa. 



The hind foot is wholly plantigrade and comparatively primitive. 

 The toes, five in number, are long and slender, bearing small, delicately 

 formed claws. The principal modification of the foot consists in the 

 greater development of the two outer digits, IV and V, which are 

 nearly equal in functional importance (see Plate LXIII, fig. r)^ and are 

 much stouter than the others, suggesting the modification in the hind 

 foot of some of the marsupials, especiall,v the wombat. The cuboid 

 is also unusually large and broad. 



This most extraordinary twist of the tibia and consequent peculiar 

 position of the hind foot is so radically difl'erent from that of mannnals 

 in general as almost to appear abnormal, but a possible explanation 

 seems to suggest itself in the manner in which the foot may have been 

 used. The fore feet and limbs so highly specialized and modifled for 

 digging, indicate that the habits of the animal were f ossorial to a high 

 degree. The principal function, therefore, of the hind limbs and feet 

 may well have been for the purpose of removing the eartli loosened 

 and thrown backward under the bod}^ l)y the enormous claws of the 

 fore feet. For this purpose the feet could be most effectively used in 

 the position above indicated, and the outer toes thus being employed 

 for the greater amount of work would naturall}' be the more strongly 

 developed. 



The outline restoration, figure (p. 634), was made from careful 

 measurements of the bones, and indicates fairly well the general char- 



