Peterson : Description of Stenomylus. 



297 



fossa very soon fades away on the fibular face of the shaft. The 

 cnemial keel is very prominent, but proportionally shorter than in 

 Oxydactylus ; a character which again more nearly approaches the 

 recent forms. The distal end is considerably expanded transversely. 

 The articular facets for the astragalus are nearly in a straight fore-and- 

 aft direction, as in the recent forms, and are divided by a prominent 

 ridge much as in these. The fibula, or external malleolus, is not pres- 

 ent in the type specimen. 



Tarsus. — The tarsus is very high and narrow and in general pro- 

 portions quite similar to that in Oxydactylus longipes. The shaft of 

 the calcaneum in Stenomylus gracilis is thinner along the plantar 

 border than in Oxydactylus. There is also a more decided prominence 

 on the plantar angle immediately back of the 

 facet for the cuboid, which causes a greater 

 antero-posterior diameter of the calcaneum at 

 this point than in the latter genus ; otherwise 

 there is little or no difference, except in the 

 size of this bone, in the two genera. The 

 astragalus is high and narrow. The external 

 condyle is larger and higher than the internal, 

 which gives a slight asymmetry to the prox- 

 imal trochlea. The internal portion of the 

 facet for the navicular is slightly less convex 

 transversely than in Oxydactylus and the recent 

 forms, but the distal trochlea is otherwise 

 similar to the camels generally. The cuboid, 



as in Oxydactylus longipes, has a large plantar hook. This gives to 

 the bone an unusually great antero-posterior diameter, while the 

 transverse diameter is small. The proximal face is taken up by 

 the facets for the calcaneum and astragalus in a more nearly equal 

 proportion than in Oxydactylus. In the latter the plantar portion of 

 the astragalar facet terminates in an ascending hook, which is forced 

 farther inward than in the genus here described. In the recent form 

 ( Camelus bactrianus) the cuboid has no plantar facet for the astragalus, 

 as the ascending hook, represented in the older genera, has become 

 entirely separated from the calcaneal facet by a deep excavation, and 

 the hook is lateral and has an articular facet for the navicular on the 

 tibial face. The general proportions of the navicular are very similar 

 to that in Oxydactylus longipes and the only noticeable difference is a 



Fig. ii. Anterior and 

 tibial views of calcaneum 

 of Stenomylus gracilis. 

 Type No. 1610. \ nat. 

 size. 



