188 ANATOMY OF THE WOOD EAT 



there are bound to be certain basic, functional differences 

 found between the fore and hind limbs. The scapula, and 

 through it the entire arm, may be moved in various direc- 

 tions, assisting, from a mechanical viewpoint, especially in 

 adduction, abduction and rotation of the whole arm. Hence 

 there are notably few adductors and abductors operating 

 directly upon the humerus or second segment. The ones 

 present are not lacking in strength, but the mobility of the 

 scapula precludes the necessity for very many muscles 

 transmitting a complexit}^ of movement to the humerus 

 such as is needed by the femur. 



It will also be noted that the flexors of the humerus are 

 many, while the femur has few, and that the extensors of 

 the former are few, while the latter has many. This is, of 

 course, natural, the arrangement being conducive to the 

 strength needed in locomotion, during which the humerus 

 is flexed while the femur is extended. There are probably 

 few actions in the life of the average mammal necessitating 

 strong extension of the arm. All that is really needed is 

 sufficient strength for quick recovery to overcome inertia 

 following flexion of this member. Quickness would be of 

 greater advantage than power, and for the former the 

 extensor muscles of the humerus are excellently placed. 

 The flexors of the femur seem to be more powerful than the 

 extensors of the humerus, as discussed shortly. 



The flexors of the third segment or forearm are notably 

 few as compared to those of the lower leg. This fact, too, 

 conforms to our expectations. Both the long and short 

 direct flexors are of moderate size, and but a fraction of the 

 bulk of the triceps series, which is the muscle mass for 

 extension antagonistic to the biceps and its accessory, the 

 brachiahs. These facts make for added proficiency in 

 running, climbing, digging and such work. Several 

 muscles which might be expected to constitute indirect 

 flexors of the forearm probably have no such action, or to an_ 



