EXTERNAL PABTS OF BIRDS. — THE FEET. 



125 



scarcely ever have more, and the principal lessenings of the number result from the absence 

 of one or two toes, or a slight reduction in the number of the joints of some toes, or absence of 

 the knee-cap. Of the normal twenty, fourteen are bones of the toes; one is an incomplete 

 bone connecting the hind toe with the foot ; one is the knee-cap, and four are the principal 

 bones of the thigh (1), leg (2), and foot (1). The first or uppermost is the thigh-bone or 

 femur (Lat. femur ; adjective, femoral), fm, from hip to knee, J. to 5 in the figure. It is 

 a rather short, quite stout, cylindrical bone, enlarging above and below. Above it has a 

 globular head, a, standing off obliquely from the shaft, received in the acetabulum (Lat. aceta- 

 bulum, a kind of receptacle) or socket of the hip, and a prominent shoulder or trochanter, 

 which abuts against the 

 brim of the acetal>ulum. Ji 



Below, it expands into 

 two condijles (Gr. k6v8v- 

 Xo?, a knob), for articu- 

 lation with both the 

 bones it meets at the 

 knee. It is the same 

 bone as the femur of a 

 quadruped or of man, 

 and corresponds to the 

 humerus of the wing. 

 In the knee-joint, many 

 or most birds have a 

 small ossicle, and a few 

 have two such bony nod- 

 ules, not shown in the 

 figure, but nearly in the 

 position of the letter B : 

 the knee-pan or knee- 

 cap, jyaiella (Lat. patel- 

 la). The thigh is the 

 first segment oi \.h.e limb; 

 the next segment is the 

 leg proper, or crus (Lat. 

 crus, the shin ; adjective, 

 crural), 5 to C in the 

 figure, or from knee to 

 heel. This segment is 

 occupied by two bones, 'i^^Z-li 

 the tibia (Lat. tibia, a 

 tube, trumpet), tb, and 

 fibula (Lat. fibula, a 

 splint, clasp), fi. Of 

 these the til)ia is tlie 

 principal, larger, inner 

 bone, running quite to the heel ; the fibula is smaller, and (with rare exceptions, as in some of 

 the penguins) only runs part way down the outside of the tibia as a slender pointed spike, close 

 pressed against or even partly fused with the shaft of the tibia. Above, at the knee, both 

 bones articulate with the femur ; tlie tibia with both the femoral condyles, the fibula only with 

 the outer condyle. Above, the tibia has an irregularly expanded head or cnemial process (Gr. 



n a (luck. Clangiila islandica, % nat. 

 knee: C, heel or ankle-joint; D, 

 ; -B to C, crus, leg proper, " drura- 



FiG. 34. — Bones of a bird's hind limb: fro 

 size ; Dr. K. W. Shufeldt, U. S. A. A, hip: B. 

 bases of toes. A to li, thigh or " second joint ' 

 stick," often wrongly called " thigh " ; C to D, metatarsus, foot proper, correspond- 

 ing to our instep, or foot from ankle to bases of toes; in descriptive ornithology 

 the tarsus; often called "shank." From D outward are the toes or digits, fm. 

 tibia, principal (inner) bone of leg ; Ji, fibula, lesser (outer) bone of 

 leg; mt, principal metatarsal bone, consisting chiefly of three fused metatarsal 

 bones; am, accessory metatarsal, bearing \t, first or hind toe, with two joints ; 2/, 

 second toe, with three joints; Zt, third toe, with four joints; 4/, fourth toe, with 

 five joints. At r there are in the embryo some small tarsal bones, not shown in 

 the figure, uniting in part with the tibia, which is therefore a tihio-tarsus, in part 

 with the metatarsus, which is therefore a tai-so-mefatnrsus ; the ankle-joint being 

 therefore between two rows of tarsal bones, not, as it appears to be, directly be- 

 tween tibia and metatarsus 



