Page:First course in biology (IA firstcourseinbio00bailrich).pdf/498

 splint bone], 8 wrist bones [7 ankle bones], 5 palm bones [5 bones of instep], 14 finger bones [14 toe bones]. The shin bone is the larger bone between knee and ankle. The long, slender splint bone and the shin bone are bound side by side.

Differences between Arm and Leg.—There is a saucer-like bone, called the kneecap, embedded in the large ligament which passes over each knee. There is no such bone in the elbow. There is one less bone in the ankle than in the wrist, hence there are the same number of bones in the arm and leg. The shoulder joint is more freely movable than the hip joint. The fingers are longer and more movable than the toes; the thumb moves far more freely than the big toe. The instep is much stronger than the palm; for each instep must support, unaided, the weight of the whole body at each step, with any other weight that the person may be carrying. The palm is nearly flat, but the instep is arched to prevent jars. When the weight of the body is thrown on the foot at each step, the top of the arch is pressed downward, making the foot longer than before. The arch springs up when the weight is removed (Exp. 1).

The Shapes of Bones.—Write L, F, or I after these names (see Fig. 28, etc.), according as the bones are long, flat, or irregular: face, cranium, vertebra, hip, rib, breastbone, collar bone, shoulder blade, upper arm bone, lower arm bones, wrist, palm, fingers, thigh bone, shin bone, splint bone, ankle, instep, toes, kneecap.