XIII 



PHYLUM CHORDATA 



381 



ment shows that the pulley-like distal end of the bone (Fig. 1049, 

 tl.l) consists of the proximal tarsals astragalus and calcaneum 



which at an early period unite with the 

 tibia and give rise to the compound 

 shank-bone of the adult. The fibula 

 (fi.) is very small, much shorter than 

 the tibia, and tapers to a point at its 

 distal end. 



Following the tibio-tarsus is an 

 elongated bone, the tarso-metatarsus 

 (Fig. 1048, ts. mtts.), presenting at its 

 proximal end a concave surface for the 

 tibio-tarsus, and at its distal end three 

 distinct pulleys for the- articulation of 

 the three forwardly-directed toes. In 



pat 

 cn.pi 



ti.ts - 



-/* 



ph.* 



mtl 



FIG. 1049. Columba livia. Part of left foot of an 

 unhatched embryo (magnified). The cartilage is 

 dotted, mtl.2, second, mtl.3, third, and mtl.4, 

 fourth metatarsal ; ti. tibia ; tl. 1, proximal tarsal 

 cartilage ; tl. 2, distal tarsal cartilage. (From 

 Parker's Zootomy.) 



the young Bird the proximal end of 

 this bone is a separate cartilage (Fig. 

 1049, tl.2), representing the distal 

 tarsals, and followed by three distinct 

 metatarsals, belonging respectively to 

 the second, third, and fourth digits. 

 Thus the ankle-joint of the bird is a 

 mesotarsal joint, occurring, as in the 

 Lizard, between the proximal and 

 distal tarsals, and not, as in Mammals 



[G. 1048. Columba livia. 

 Bones of the left hind-limb. 

 cn.pr. cnemlal process ',fe. femur ; 

 fi. fibula ; hd. head of femur ; 

 mtts. J, first metatarsal ; pat. 

 patella ; ph.l, phalanges of first 



digit; ph. 4, phalanges of fourth (q.v.), between the tibia and the proxi- 

 mal tarsals. To the inner or pre-axial 

 side of the tarso-metatarsus, near its 



., 



digit ; ti. ts. tibio-tarsus ; ts. 

 mtts. tarso-metatarsus ; tr. tro- 

 chanter. 



distal end, is attached by fibrous tissue a small irregular bone, the 

 first metatarsal (Fig. 1048, mtts. 7). The digits have the same 



