COISTDYLARTHRA. 389 



The base of the diapophysis of the atlas is perforated as in the suc- 

 ceeding cervicals. The Literal perforating foramen is entirely isolated. The 

 axial facets are separated. The axis is depressed and moderately short. 

 The odontoid is depressed, and has an oval section. The cervical vertebrae 

 -are much shorter than in Phenacodus, being deeper than long, and wider 

 than deep. They are very slightly opisthoc^lous. The caudal vertebrae 

 are quite robust, indicating a powerful tail. Dorsals not found. 



The tubei'osities of the humerus are small in proportion to the size of 

 the head. The condyle is much like that of a creodont, with internal flange 

 and external cylinder, without intertrochlear crest or ridge The internal 

 epicondyle is large, and is pierced above by an epitrochlear foramen. The 

 olecranon is compressed. The head of the radius has a flat articulation with 

 the ulna. Its outline is a transverse oval, narrowed at the external extrem- 

 ity. The scapula has a well developed coracoid hook, and the spine rises 

 abruptly from the neck. 



In the P. rhabdodon the femur is not materially larger than the hume- 

 rus. The great and little trochanter are well developed, and the third tro- 

 chanter is situated low down, as in Phenacodus, and not opposite the little 

 trochanter as in C'reodonta. 



The posterior foot has five digits. The astragalus is much like that of 

 the Prohoscidea in form. The head is moderately long, and is depressed. 

 Its distal extremity is regularly convex from side to side. The trochlea is 

 borizontal, and is not grooved medially, but is very slightly concave. Fib- 

 ular face vertical; malleolar fixce slightly oblique and occupied by a deep 

 central fossa. The head is not as convex as in Phenacodus, but is more 

 recurved on both sides. On the external side it is so far recurved as to be 

 continuous (in P. rhahdodon) with the sustentacular facet, and a part of this 

 face is probably in contact with the cuboid, as in many creodonta, but which 

 cannot be said therefore to overlap the astragalus, as in the Anddypoda. If 

 this facet were distal, and in the plane of the navicular facet, it would be 

 necessary to refer this genus to that order. 



The calcaneum is robust. Its astragalar facets, especially the external, 

 are rather flat. The cuboid facet is large, and is supplemented by an 

 external tuberosity. The sustentaculum is well developed. Free portion 



