18 



M. 



Diameter proximal eud, (condyles) - - - -044 



Length radins 220 



TraUwSverse diameter (proximally) - '045 



Transverse diameter (at middle) - - 026 



Transverse diameter (distally) 038 



Anteroposterior diameter (proximally) 025 



Anteroposterior diameter (medially) 018 



Anteroposterior diameter (distally) 023 



Diameter femur, (shaft) 040 



Diameter femur (condyles) 058 



Length tibia - - - - - -250 



Length foot including tarsus • . • • • -325 



Length foot without tarsus 277 



Outside length of calcaneum 075 



Depth of calcaneum behind 027 



"Width of calcaneum in front 033 



Total length astragalus 045 



Total width astragalus - 041 



Width trochlea astragalus 018 



Width navicular facet 022 



Depth navicular facet , - - • 022 



W^idth cuboid facet • ■ -008 



W^idth cuboid bone fore and aft - -023 



Length cuboid bone 015 



Length internal metatarsus 170 



Transverse width trochlea of median metatarsus 021 



Length pastern 042 



Width posterior (proximally) 025 



Length coronet 027 



Width coronet (proximally) - - - - .025 



Length coffin 036 



Width articular face 021 



W^idth between angles 030 



Elevation behind - - - -023 



Eemarlcs. Professor Leidy has already observed that the structure of 

 the molars in this genus is in its type the same as that of the deciduous 

 molars o? J3c[uus^ and that hence, that FrotoMppiis represents the more 

 primitive condition of horse. In further confirmation of this view, I may 

 add that the proportionate size of the head and length of limbs to size 

 of body is greater in this S])ecies than in the recent species of Equus, 

 resembling in these points the colts of that genus. Acceleration of the 

 "■rowth of the body and prolongation of the face, the same in the widen- 

 ing (tore and aft; of the internal columns of the molar teeth, with re- 

 tardation of the growth of the lateral phalanges, would express the pro- 

 cess of evolution of the modern types of horse. 



PnoTOHiPPUS PERDITUS Laidy, 



Eepresented in the collections by the entire molar dentition of one cran- 

 ium ; the greater part of that of another with incisors and canines ; the 

 four median molars of another, two superior molars with mandible and 

 teeth of a fourth ; mandibular dentition of a fifth, with parts of mandi- 

 bles and symphyses and isolated molars of a large number of other 

 specimens. 



