IN THE LIMBS OF MAMMALIA. 25 



upon the nearer half and thus between the power and the fulcrum, when it would be a 

 lever of the second kind. 



Of course, any obliquity in the direction of the muscle or bone, or any variation in the 

 shape of the rotated bone or limb, or the presence of any part as the hand, which may be 

 appended to the extremity, will only appear to complicate the motion without essentially 

 affecting its character. 



The general law, according to which the muscles of the mammalian limb seem to be 

 arranged, is in no way startling or peculiar, and the only wonder is that it has never been 

 observed before. No new facts are required for its illustration ; human anatomy contains 

 the great bulk of the material, though of course aided by comparative anatomy; and it 

 needs only to see that the facts are not arbitrary, but bear such mutual relation as clearly 

 to admit of one general statement. I will commence with the muscles which act upon the 

 fore-arm, that segment of the anterior extremity in which I first detected the arrangement, 

 and in which it is quite closely adhered to. 



There are two direct flexor muscles of the fore-arm : one is the biceps arising from 

 the scapula and inserted into the radius, the other is the brachialis anticus arising from the 

 humerus and inserted into the ulna, though both, of course, are attached to one and the 

 same segment, fore-arm. But this segment may be also flexed indirectly by the ulnar and 

 radial extensors of the wrist ; for when a joint is partially or wholly fixed by the simul- 

 taneous contraction of antagonist muscles on opposite sides, then the two segments between 

 which the joint intervenes become teleologically as one segment, which is acted upon by all 

 muscles arising from any other segment, and inserted into either of them; each segment 

 being acted upon directly by the muscles which are attached to itself, and indirectly by those 

 attached to the other. The fore-arm is directly extended by two muscles, one short, the 

 humeral heads of the triceps, and the other long, the scapular head of the same ; the indirect 

 extensors are the ulnar and radial flexors of the wrist, commonly called extensores carpi ul- 

 naris and radialis. 



The humerus is flexed upon the scapula by three muscles, directly by two, one short, 

 teres major, arising from the scapula, and one long, arising upon the side of the body, 

 latissimus dorsi ; and indirectly by the third, the scapular head of the triceps which is also the 

 long direct extensor of the segment next below. 



How is it now with the corresponding segments of the posterior extremity ? The leg is 

 flexed at the knee, directly by two sets of muscles, one of which is represented by the popli- 

 tceiis with the short head of the biceps when it exists, the former corresponding with the 

 short direct flexor of the fore-arm, brachialis antkus ; the other set is composed of the long 

 head of the biceps with its accessories, the semi-tendinosus and semi-membranosus, the former 

 corresponding with the long direct flexor of the fore-arm, biceps himicri ; while the peronceus 

 long us and tibialis posticus, with their accessories; the muscles composing the calf of the leg, 

 and which are long direct extensors of the foot, are, if the ankle-joint is fixed, the indirect 

 flexors of the leg, the segment next above, and correspond thus with the extensores carpi 

 and the palmaris in the other extremity. 



7 



