x. 
EXTERNAL PARTS OF BIRDS.—THE FEET. 119 
searcely 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 
Jemur (Lat. femur ; adjective, femoral), fm, from hip to knee, A to B 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 acetabulum. 
Below, it expands into 
two condyles (Gr. xévdv- 
Ros, 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, patella (Lat. patel- 
la). The thigh is the 
first segment of the limb; 
the next segment is the 
leg proper, or crus (Lat. 
crus, the shin; adjective, 
crural), B to C in the 
figure, or from knee to 
heel. This segment is 
‘oceupied by two bones, 
the tebia (Lat. tibia, a 
tube, trumpet), tb, and 
Jibula (Lat. fibula, a 
splint, clasp), fi. Of 
these the tibia is the 
principal, larger, inner 
PALE 
Fig. 34.— Bones of a bird’s hind limb: from a duck, Clangula islandica, 3 nat. 
size; Dr. R. W. Shufeldt, U.S.A. A, hip: B, knee: C, heel or ankle-joint; D, 
bases of toes. A to B, thigh or “second joint’; Bto C, crus, leg proper, “ drum- 
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. 
femur; ¢b, tibia, principal (inner) bone of leg; fi, fibula, lesser (outer) bone of 
leg; mt, principal metatarsal bone, consisting chiefly of three fused metatarsal 
bones; am, accessory metatarsal, bearing 1t, first or hind toe, with two joints; 2¢, 
second toe, with three joints; 3¢, third toe, with four joints; 4¢, fourth toe, with 
five joints. At C there are in the embryo some small tarsal bones, not shown in 
the figure, uniting in part with the tibia, which is therefore a tibio-tarsus, in part 
with the metatarsus, which is therefore a tarso-metatarsus ; the ankle-joint being 
therefore between two rows of tarsal bones, not, as it appears to be, directly be- 
tween tibia and metatarsus. 
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; the tibia with both the femoral condyles, the fibula only with 
the outer condyle. Above, the tibia has an irregularly expanded head or enemial process (Gr. 
