PHENACODUS. 483 



unequal, and the head not so flat and laterally extended. The depth of the 

 navicular face is two-thirds the transverse length, while in P. primcevus it is 

 about half the same. Its convexity is flattened in the P. vortniani, but 

 entirely convex in P. primoevus. Its surface is strongly recurved on the 

 internal side as in that species. The median fossa of the internal face of 

 the trochlear portion is distinct. The inferior anterior angle of the external 

 side of the same is flared outwards, as in P. primcevus. 



The calcaneum, like the bones of the leg, is rather more slender than 

 that of P. primoivus. It resembles that element of the latter in most respects, 

 but the cuboid face does not present the internal angle, but is truncate next 

 the astragalus. It is quite oblique, both in the transverse and the vertical 

 direction. The cuboid is like that of P. primcevus, but is less robust. The 

 navicular also resembles that of the same animal. The part of its distal face 

 which is applied to the ectocuneiform is convex, to fit the proximal con- 

 cavity of that bone. Its posterior down-looking tuberosity is well devel- 

 oped. The ectocuneiform and mesocuneiform are relatively more elongate 

 than in P. primcevus. The latter is quite flat in P. primcevus, but its length 

 in P. vortmani equals its width at the second metacarpal. On the other 

 hand the entocuneiform is shorter than that of P. primcevus, and its inferior 

 border is compressed, and little or not at all truncate. The metatarsal facet 

 is, on the contrary, quite strong in the P. primoevus. 



The metatarsals are all rather more slender than those of P. primcevus. 

 The fourth is as long as the calcaneum in P. vortmani, but is shorter than 

 that element in P. primcevus. When in place it is not quite as much pro- 

 duced as the second in P. vortmani; in P. primcevus it reaches the same 

 point on the third. The second is produced proximally more than the others, 

 and hence has a lateral facet for the ectocuneiform. The relative lengths 

 of the toes are, beginning with the shortest, I, V, IV, II, III, as in P. pri- 

 mcevus. The fifth is half as long as the third; it has two proximal articular 

 facets; one lateral, the other proximal for the cuboid. The first has a sin- 

 gle narrow proximal facet. The distal articulations are not so stout as in P. 

 primcevus, but the distal posterior keels are well developed. The ligamen- 

 tous fossse are well defined. 



The first metatarsal is somewhat flattened, and its shaft is divergent 



