73° 



THE POPULAR SCIENCE MONTHLY. 



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. 



Fig. 9.— S, rectus steraalis or skin muscle, superficial to the great pectoral muscle of chest. 



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 develop- 

 ment 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 {hrachi- 

 alis miticiis), which helps to bend the elbow, and the other to the 

 outer side [supinator longus), which suj^inates 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 to- 

 gether by muscular fibers. This is the normal arrangement in apes 

 and monkeys, the union of these two muscles aiding them greatly 



