38 THE DESEADO FORMATION OF PATAGONIA 



navicular, and a shallow saddle-like one below for Mt. 

 II, which is entirely carried by this bone. 



The ectocuneiform is considerably larger than the meso- . 

 cuneiform, resting above on the navicular, and carrying 

 below the whole of Mt. III. On its inner side are two 

 facets which rub against the upper end of Mt. II. 



The cuboid is a nodular bone, its upper surface occupied 

 by the facet for the calcaneum, the lower face occupied by 

 the facet for Mt. IV, while on the external side 

 there is a tiny beveled facet for the vestige of 

 Mt. V, and with a small boss on the inner 

 surface which carries two tiny facets, the upper 

 Fig. 12. cuboid one for the ectocuneiform and the lower for the 



internal side to 



navicular. On this same inner side, near the 



for navicular ^c top there is a second small boss, which carries 

 tilr & tiny facet to rub on the astragulus, and 

 fecetfar below that a second tiny facet for the navicular. 



mesocunieforms r^i . r , .. . . . . 



i/2 natural I he pes consists of three digits, with a vestige 

 of Mt. V. Of the developed digits, the median 

 one is the largest, but the two lateral digits are only a little 

 smaller and were functional, so that this form was truly 

 three-toed, comparable in the digital reduction to Meso- 

 hippus. 



Mt. II is flattened above but soon broadens into a 

 rounded shaft of considerable length, on the end of which 

 is the articular trochlea, with the carina extending onto 

 both the upper and lower surface, being, however, higher 

 on the lower surface. Proximally this bone is overlapped 

 by the endocuneiform, is carried by the small mesocunei- 

 form, and also articulates on the inner side of the ecto- 

 cuneiform. Mt. Ill is also compressed at the upper end, 

 broadens below, and carries an articular trochlea similar 

 to that of Mt. II, except that the carina does not extend 

 so far onto the upper surface. Like Mt. II, Mt. IV is 

 carried high on the tarsus, and therefore, though nearly as 

 long as Mt. Ill, it does not have the same effective length. 



