(iKE(;()iiY: xoTiiAh'cras, an American eocene primate 



99 



shaft is Hattened, soinetimes bearing a roughened peroneal si)ine bel(n\' the ectal facet. Between this 

 spine and the sustentacuhim is a prominent groove for the flexor longiis halhieis. The posterior surface 

 near the lower end bears a tuberosity for the attachment of the short plantar ligament. 



Thus the calcaneum of Notharctus is only a little less specialized for arboreal leaping than is that of 

 Lemur, the chief difference being that the sustentaculum tali is nearer the lower end than it is in the 

 modern genus. 



Cuboid 

 PlaUs XXX, XXXI 



The cuboid of Notharclus is eciually leniuroid in type. It is flattened dorsoventrally, is subrectangular, 

 with the long axis continuous with that of the calcaneum. The cuboid affords a firm base for the cal- 

 caneum and receives the lateral thrusts of the navicular and ectocuneiform. It rests in turn upon digits 

 IV and V. There is but little motion between the cuboid and the elements around it. It can twist upon 

 the lower end of the calcaneum by means of a subconical elevation which is received into a correspond- 

 ing depression of the lower end of the calcaneum. It abuts laterally against the navicular and ectocunei- 

 form by means of flattened or slightly convex articular surfaces. Externally it bears a prominent pro- 

 jecting tubercle which is deeply grooved by the tendon of the long peroneal muscle; this tendon prevents 

 lateral displacement of the cuboid. On its lower or posterior face the cuboid is tied to the calcaneum by 

 the calcaneo-cuboid ligament. The groove for the peroneus longus passes obliciuely downward and 

 inward across the posterior face of the cuboid, and is covered by the cubo-metatarsal ligament. • The 

 concave distal end receives the coua'cx facets of metatarsals IV and V. 



The principal difference from the cuboid of Lemur is that in Notharelus this element is narrow trans- 

 A'crsely in proportion to its height. 



Navicular 

 Plate XXX; Text Fi-. 22 



This bone forms a base for a system of converging elements, which comprises the three cuneiforms 

 and their attached digits. Thus it receives the thrusts from these elements below and from the cal- 

 caneum above. The bone slants sharply inward, backward and downward in such a way that its under 

 surface flanks medially the tleej) gutter for the flexor tendons on the under side of the tarsus. But the 

 slanting position of the na\'icular is especially connected with the turned-in position and the thuml> 

 like character of the hallux. On the under side, the navicular is held in place especially by the.«strong 

 wide tibio-navicular ligament, which runs from the proximal, internal tip of the navicular beneath the 

 head of the astragalus to the sustentaculum tali and to the lower end of the internal malleolus. The 

 navicular abuts against the cuboid laterally by a flat facet on its outer side at the lower end. On its 

 front surface, immediately above the ectocuneiform, it bears a low rounded eminence to which is attached 

 the scapho-cuneiform ligament. This eminence is more pronounced in Xolhoretu^i than it is in Lemur. 

 Just above the facet for the entocuneiform on the posteroinferior corner of the bone, there is a smooth 

 articular siu'face for the tendon of the tibialis posticus muscle which is inserted on the under side of the 

 navicular and on the dorsointernal rim of the entocuneiform. 



The surfaces and facets of the navicular of Notharctus are all peculiarly lemurine in type. It lias a 

 deeply concave facet above for the head of the astragalus and this concave border runs dorsointernally 

 into a process for the attachment of the tibio-navicular ligament. The bone bears below a triad of facets. 



