78 Annals of the Carnegie Museum. 



tends much beyond the tibia, causing the external malleolus of the leg 

 to be the lower of the two. 



The Tarsus. As in all other simians and apes, we find in the tarsus 

 of Lasiopyga and Callithrix the seven usual bones, and these have 

 practically the same relative size, and articulate in much the same 

 manner as in Homo. When Hgamentously articulated as in life, they 

 form a plantar double arch, an antero-posterior one, and a transverse 

 one. We also find in the foot of each of these genera the paired 

 sesamoids on the plantar aspect, beneath the metatarso-phalangeal 

 articulations as in the manus; but they appear to be absent from the 

 more distal joints. There is also in these genera another sesamoid 

 present, which I fail to find elsewhere described for the apes, although 

 it may have, and probably has, been described. It occurs in both 

 Lasiopyga and the marmoset, and consists in a somewhat sizeable 

 segment, semiellipsoidal in form, and articulates with the postero- 

 external angle of the cuboid, being embedded in the tendon of the 

 peroneus longus muscle as it passes this point on its way to its inser- 

 tion at the infero-posterior internal angle of the base of the meta- 

 tarsal of the hallux. It may be conveniently named the peroneal 

 sesamoid. 



Most of the observable departures in the form of the podial bones 

 from those in man are due to the peculiar twisting of the foot in the ape. 

 Both the astragalus and the calcaneum are rather large bones with 

 extensive articular surfaces, the posterior moiety of the latter being 

 concave on its inner side and slightly bent in that direction. The 

 area for the insertion of the tendo Achillis on its hinder aspect is 

 abruptly defined by a sharp line. The anterior articular surface of the 

 OS calcis for the scaphoid or navicular bone is concave; whereas the 

 corresponding facet on the astragalus is convex. The cuboid and 

 scaphoid are of about the same size, and articulate with each other in 

 the middle line of the foot. The middle cuneiform is the smallest of 

 the three cuneiform bones, while the saddle-shaped ectocuneiform and 

 the scaphoid dip down far below all the others in the sole of the foot. 

 Mivart has described in his article in the Encyclopaedia Britannica 

 many of the characters of the tarsal bones and phalanges, and com- 

 pared their proportions, especially for Simia, A teles, Hylohates, 

 Pithecia, Troglodytes, Lagothrix and Cebus, but has little or nothing to 

 say of Lasiopyga and Callithrix. The morphology of the tarsus in the 

 latter is much the same as we find it in L. callitrichus. 



