Page:Popular Science Monthly Volume 25.djvu/748

730 exist normally, but in a much more highly developed state; they are especially well seen in animals which use their fore-limbs for digging, climbing, or swimming. In them the muscle is of large size, and reaches to the inner edge of the lower extremity of the arm-bone; in man, when it reaches thus far, it is only rudimentary and of no use.



Another muscle which I have seen in about three per cent of human subjects is a small one which goes from the breastbone to the upper end of the shoulder-blade. This muscle is well developed in animals which have no collar-bones; it reaches its highest development in the horse, pig, hippopotamus, and elephant. It is also seen in the Guinea-pig, Norway rat, and wombat. It is quite rudimentary when it exists in man, and serves no useful purpose.

In man, near the elbow-joint, and lying close together, are two muscles going from the upper to the lower arm; one in front (brachialis anticus), which helps to bend the elbow, and the other to the outer side (supinator longus), which supinates or twists the fore-arm outward. As a rule, these muscles are quite distinct, though they lie side by side; but in about one per cent of cases they are joined together by muscular fibers. This is the normal arrangement in apes and monkeys, the union of these two muscles aiding them greatly