SEC. HI EXTERIOR PARTS OF BIRDS 177 



is the knee-pan or knee-cap, patella (Lat. patella). The thigh is the 

 first segment of the limb ; the next segment is the leg proper, or 

 aus (Lat. cms, the shin ; adjective, crural), B to C in the figure, or 

 from knee to heel. This segment is occupied by two bones, the 

 tibia (Lat. tibia, a tube, trumpet), tb, and fibula (Lat. fibula, a splint, 

 clasp), _^. Of these the tibia is the 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 ; the tibia with both 

 the femoral condyles, the fibula only with the outer condyle. 

 Above, the tibia has an irregularly expanded head or cnemial pro- 

 cess (Gr. Kvrifiri, kneme), which in some birds, as loons, runs high 

 up in front above the knee-joint. Below, the tibia alone forms the 

 ankle-joint, C, by articulating with the next bone: For this purpose 

 it ends in an enlarged trochlear (Gr. Tpoxo-^ta), or pulley-like surface, 

 presenting a little forward as well as downward, above which, in 

 many birds, there is a little bony bridge beneath which tendons 

 passing to the foot are confined. This finishes the leg, consisting 

 of thigh, A B, and leg proper, B C, bringing us to the ankle-joint 

 at the heel, C. 



Now a bird's legs, unlike ours, are not separate from the body 

 from the hip downward ; but, for a variable distance, are enclosed 

 within the general integument of the body. The freedom of the 

 limb is greatest among the high perching birds, and especially the 

 Baptores, which use the feet like hands, and least among the lowest 

 swimmers. The range of variation, from greatest freedom to most 

 extensive enclosure of the limb, is from a little above B nearly to C — 

 the latter in the case of a loon, grebe, or penguin. In no bird is 

 the knee, B, seen outside the general contour of the plumage : it 

 must be looked or felt for among the feathers, and in most prepared 

 skins will not be found at all, the femur having been removed. It 

 is a point of little practical consequence, though bearing upon the 

 generalisation just made. The first joint, or bending of the- limb,, 

 that appears beyond a bird's plumage is the heel, or sufrago, C ; and 

 this is what, in loose popular parlance, is called "knee," upon the 

 same erroneous notions that make people call the wrist of a horse's 

 fore-leg " knee." People also call a bird's aus or leg proper, B to 

 G, the " thigh," and disregard the true thigh altogether. This con- 

 fusion is inexcusaftile ; any one, even without the slightest anatomical 

 knowledge, can tell knee from heel at a glance, whatever their 

 respective positions relative to the body. Knee is at junction of 

 thigh and leg proper ; it always bends forward ; heel is at junction 

 of leg with foot, and always bends backward. This is as true of a 



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