Figure 4: Left humeri in anterior view.
From: Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India

(a) Phenacodus vortmani (USGS 7159). (b) Cambaytherium thewissi (GU 7006). (c) Homogalax protapirinus (USGS 25032), to same scale. CAP, capitulum; CT, capitular tail; DPC, deltopectoral crest; ENT, entepicondyle; ENT F, entepicondylar foramen; LAT SUP R, lateral supracondylar ridge; ST FOR, supratrochlear foramen. Entepicondylar foramen (Phenacodus only), distally extensive deltopectoral crest, rounded capitulum and prominent lateral supracondylar ridge are primitive traits. Cambaytherium and the primitive perissodactyl Homogalax are derived in losing the entepicondylar foramen, and Homogalax is further derived in being more elongate, with reduced deltopectoral and lateral supracondylar crests, and a conspicuous capitular tail. Scale bar, 1 cm.