1881.] - on the Feet of Mammalia. 547 
flexure of the joint. (2) They fit entering grooves of the proxi- 
mal ends of corresponding bones. These will be the result of the 
same application of force and displacement, as the protrusion of 
the inferior, commencing with a concavity (Elephas); becoming 
Fic. 9. ~ Fic. 10. | Fig 11. 
Fic. 9.—Part of anterior foot of Procamelus occidentalis from New Mexico, From | 
Report of Capt. G. M. Wheeler, Vol. Iv, Pt. 1. 
Fic. 10.—Metacarpals of Cosoryx furcatus from Nebraska, two-thirds natural size; 
a, anterior face; 4, posterior; c, proximal end; d, distal end. 
Fic, 11.—Left forefoot with part of radius of Poédrotherium vilsoni Leidy, from 
Colorado, three-fifths natural size. From Hayden’s Report, Iv. 
more concave (Fig. 7), and becoming finally a groove. (3) When 
the dense edge of a bone, as in the case of the lateral walls of the 
astragalus, is presented upwards, a groove is produced in the 
