526 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



M. 



Length from first incisor to orbit 0.198 



Diameter of orbit 045 



Widtli of nasals at notch 031 



Width of front at middle orbit 076 



Width of zygomata posteriorly 132 



Width between meatus - 088 



Width betv;^eeu middle molars .038 



Width of occipital foramen and condyles , 054 



Length of mandibular ramus 270 



Length from end-incisors to last molar .190 



Length from end-incisors to first molar 077 



Length from end-incisors to canine, (axial). ...l 025 



Depth of symphysis in front of foramen mentale. 028 



Depth of ramus at first premolar 043 



Depth of ramus at sixth premolar 063 



The skeleton is noteworthy for the disproportionately large size of the 

 cervical, as compared with the dorsal vertebrse. The large size of the 

 head, compared with the rest of the animal, was supplemented by the 

 length and slenderness of the limbs, which considerably exceeded the 

 proportions they bear in the existing horse. The lumbar vertebrae are 

 slightly opisthocoelian, the dorsals strongly so. The cervicals are large 

 and moderately elongate 5 the size results from the great development 

 of the processes, since the centra do not materially exceed those of the 

 lumbars. The atlas is not much expanded, and has a well-marked tu- 

 herculum atlantis and very low neural keel. 



The limbs are slender and the hoofs small. The humerus is more 

 curved than in the horse, and has a strong tubercular deltoid crest. 

 The proximal tuberosities are very different from those of the horse. 

 The external is largely developed, but is not produced into a hook nor 

 extended into a longitudinal crest. The inner bicipital tuberosity is a 

 little more prominent, and curves hook-like outward, inclosing with the 

 outer a deep notch. It is continued at right angles along the inner 

 aspect of the head into a straight crest; their angle of union is pro- 

 longed downward as the deltoid crest. The outer tuberosity in the 

 horse is double, and, while not hooked as in BMnocerus, is a little 

 more prominent than in the present species ; the inner is not hooked as 

 in the P. sejunctus. There is an ala on the inner side of the distal end 

 of the humerus, and a supracondylar foramen, both of which are want- 

 ing in the horse. 



The radius differs from that of the horse in being considerably longer 

 than the humerus instead of a little shorter. It is gently curved and 

 flattened, with the transverse ends about equally wide. The ulna is 

 co-ossifled with it throughout the length, excepting a small portion 

 beyond the humeral cotylus, as in the horse. 



The femur is stout, with the lesser trochanteric ridge well developed. 

 The trochlea is wide, with subequally elevated bounding ridges. The 

 tihia is considerably longer than the femur, and presents a long and 

 Ijrominent cnemial crest. The shaft is transverse, with external edge 

 and inner plane narrower than the anterior. The trochlea is very 

 oblique, the astragaline grooves well defined by the internal and ex- 

 ternal tuberosities. Fibula not i^reserved. 



The right posterior foot, among others, is perfectly preserved. It is, 

 like the radius and forefoot and the tibia, distinguished for its elonga- 

 tion and slender proportions, as compared with the horse. The astraga- 

 lus differs from that of the horse in having the cuboid facet on a more 

 pronounced neck, and in the narrowness of the trochlea. The navicu- 

 lar facet is subpentagonal and without emargination. The ctiioid is 

 largely extended posteriorly, where it bears a large tuberosity. The 



