102 (jregory: notharctus, an American eocene primate 



v-erse ligaments and on the plantar aspect by the deep plantar ligaments, attached to the tubercle at 

 the upper end. The bone is less warped and twisted than that of Lemur, a condition which is again 

 correlated with the sharper di\'ergence of the hallux in that genus. 



Entocuiieiform 

 Plates XXX, XXXI; Text Fi^. 22 

 The internal cunoifoi'ni affords a wide base for the very large hallux. It is typically lemuroid in 

 form, differing chiefly in the more bulging contour of its posterior surface. Its most conspicuous feature 

 is the wide concavoconvex facet for the hallux. On its front face it bears a round conspicuous tubercle 

 for the attachment of a stout ligament connecting it with the upper end of the hallux (homologous with 

 the lateral tarso-metatarsal ligaments of man), and on its rear margin it bears a prominent compressed 

 eminence with an articular surface for the tendon of the flexor longus hallucis and for the fascia of the 

 flexor brevis hallucis. The {(>xternal) side of this tuber near the base gives insertion to ligaments running 

 transversely^ to the ectocuncnform, while in front of this was a ligament that was attached to the meso- 

 c unciform. 



The facet for the luiAicular, which (X'cupies the whol(> ui)i)er surface of the bone, is concave. The 

 l)osterosuperior rim of the bone gives insertion to the tentlon of the tibialis posticus muscle. 



The entocuneiform takes part with the cuboid and with the other cuneiform bones in the forma- 

 tion of a deep gutter for the flexor tendons of the foot. It abuts laterally against the upper end of the 

 second metatarsal and against the mesocimeiform. 



Hallux 



Plates XXX, XXXI; Text Ki-s. 22, 2)5 

 As already stated, Nolhardus progressed chiefly by leaping from branch to branch, grasping the 

 l>i-aMches at the end of each leap with the hands and feet, but especially with the latter, as do modern 

 lemurs. 



The hallux of Notharctus is a highly specialized organ of locomotion which in functional importance 

 was equivalent to all the i-emaining digits together, since it constituted one half, and that the more active 

 one, of a pair of pincers, the remaining digits collectively forming the opposing and more passive half. 

 By means of the powerful flexors and of the massive adductors of the hallux the great skin pads on its 

 plantar surface were pressed against the supporting branch, while the corresponding pads on the sole 

 of the foot were pressed against the branch in an opposing direction. 



The first metatarsal ends proximally in a very large and transversely extended concavoconvex articu- 

 lar siu'face for the entocuneiform. This articular surface is guarded in front by a raised rim, culminating 

 dorsally in an obtuse process, the rim and process together giving attachment to the ligaments that fasten 

 the hallux to the entocuneiform and to the navicular respectively. The same articular surface is con- 

 tinued dorsoposterioi'ly on to the anterior face of the great process for the tendon of the peroneus longus 

 muscle. This j)rocess is markedly asymmetrical, curving upward posteromedially. Its upper end, which 

 gives insertion to the peroneus tendon, projects into the lower end of the deep gutter on the plantar sur- 

 face of the foot described above. The anterolateral portion of this peroneal process bears an articular 

 surface, marking the area of contact with the plantar surface of the second metatarsal. The presence 

 of the metatarsal element at this point and its conseciuent contact with the peroneal process limits the 



