PHENACODUS. 481 



inate bone to the posterior edge of the obturator foramen In P. primoevus 

 the tibia is a little shorter than the femur, and is six-sevenths the length of 

 the innominate bone to the posterior edge of the obturator foramen. 



The femur has mnch the character of that of P. primcevus, including 

 the transversely oval form of the head, and the large third trochanter. The 

 long axis of. the proximal extremity makes an angle of 45° with the long 

 axis of the distal extremity, but the long axis of the head is parallel with 

 that of the distal extremity. It therefore does not coincide with the long 

 axis of the proximal extremity. The latter is at right angles to the long 

 axis of the proximal extremity of the great trochanter. The latter is ob- 

 liquely truncate, so that its external angle is as high as the head, and the 

 internal angle is longer than the head. The latter sends down a strong 

 ridge which bounds the large trochanteric fossa posteroextemally. The 

 small trochanter is prominent. The rotular groove is rather narrow and 

 elevated, and the internal ridge is a little more prominent on its convexity 

 than the external. The internal condyle is narrower than the external. 

 The latter has a fossa just external to the edge of its anterior portion. At its 

 posterior base the face of the shaft has an external shallow fossa, and an 

 internal rib. The former is bounded externally by a faint ridge which 

 extends towards the great trochanter. Other than this there is no trace of 

 linea aspera. 



The patella is short and robust It is truncate above, and acuminate 

 below. Anteriorly it is convex with two proximal lateral facets. 



The tibia is rather slender. The crest is moderately prominent, and 

 continues as the obtuse angular front of the shaft. Its superior extremity 

 is truncate downwards. The spine is not prominent. The cotyli of the 

 head are not very unequal ; the internal longer fore and aft, the external 

 longer transversely. The posterior face below the head is concave, with 

 equal lateral bounding ridges. The internal ridge is the more acute, and 

 continues as the angular internal edge of the shaft to near the distal extrem- 

 ity. The internal edge of the head is acute ; the external edge is truncate 

 in front of the fibular facet. The long axis of the distal extremity makes 

 an angle of 35° with the long transverse axis of the head. The astragalar 



grooves are on the contrary parallel to the long anteroposterior axis of 

 31 c 



