No. 2.] THE RELATIONS OF PROTOCERAS. 351 



Like the astragalus, the cuboid is higher than in the recent 

 Pecora ; the calcaneal surface is relatively wider, the astragalar 

 facet narrower than in those animals. The calcaneal facet is 

 wider than the corresponding distal portion of the bone and 

 hence forms an overhanging ledge. The astragalar surface is 

 narrow and simply concave in the dorso-plantar direction ; 

 shortly behind the points where the two facets join they are 

 narrowed by a circular sulcus and another invades the astrag- 

 alar facets of both cuboid and navicular. The principal dia- 

 meter of the cuboid is the dorso-plantar, due partly to the large 

 size of the posterior hook, which is more or less rudimentary 

 in the modern Pecora. Of the inner or tibial side of the 

 cuboid about one half the height is occupied by the navicular, 

 which is supported upon two narrow, ledge-like projections, the 

 posterior one of which is considerably more prominent than 

 the anterior. Below the ledge on the dorsal side is a flat facet 

 for the ectocuneiform and there is an additional facet for this 

 bone in the middle of the cuboid. The distal surface is occu- 

 pied by the large and somewhat irregular facet for the fourth 

 metatarsal, which is convex in front and concave behind. The 

 facet for the fifth metatarsal is very small and entirely lateral 

 in position, much as in Pcsbrotherium. An additional facet 

 for the plantar projection of mt. IV is formed on the infero- 

 internal side of the cuboid hook. 



The navicular is higher than in the recent Pecora, but not 

 otherwise notably different. The astragalar surface is concave, 

 but has a low, rounded ridge near the fibular border for the 

 groove on the distal trochlea of the astragalus. On the proxi- 

 mal dorsal margin this ridge forms an elevation which is less 

 distinctly marked than in most of the existing Pecora. The 

 portion of the circular sulcus above mentioned as invading the 

 approximate astragalar surfaces of the cuboid and navicular, 

 which affects the latter, forms a channel or groove along the 

 whole fibular side of the bone. On the same side are two 

 well defined facets for the cuboid, of which that on the plantar 

 side is the larger and presents more inferiorly. On the distal 

 side are two very distinctly separated facets for the cuneiforms. 

 The anterior one, which is for the coalesced ecto- and meso- 



