116 



THE STRUCTURE OF MAN 



FIG. 73. DEEP MDSCLES ON THE FLEXOR 

 SIDE OF THE FOREARM. One-fifth natural 

 size. (After Rauber. ) 



The muscles of the upper arm, and the 

 superficial muscles of the forearm and 

 hand, with the lumbricales, are removed. 

 The position of the anterior annular 

 ligament is indicated by two dotted lines. 



hu., humerus ; p.c., processus coronoideus 

 ulnae ; l.o., the orbicular ligament ; p.s'., 

 proc. styloideus radii ; p.s"., proc. sty- 

 loideus ulnae ; e.c., eminentia carpi ul- 

 naris ; I.e., lig. accessorium cubiti mediale; 

 s., M. supinator ; /./., M. flexor longus 

 pollicis ; f.p., M. flexor profundus 

 digitorum ; p.q., M. pronator quadratus ; 

 f.b., deep head of the flexor brevis 

 pollicis ; a.p., M. adductor pollicis; i.p., 

 M. interosseus dorsalis primus ; i.d., Mm. 

 interossei dorsales et volares ; be., 

 bicipital tendon. 



the muscles round these organs. 

 It is, therefore, a fact of the 

 greatest importance that, while 

 many variations are found in 

 the muscles near the mouth 

 and the eyelids of Man, in- 

 dicative of new possibilities of 

 development, in the other Pri- 

 mates these muscles show a 

 monotonous constancy. May 

 it not also be possible that still 

 more subtle differences occur 

 between the various human 

 races in the detailed arrange- 

 ment of the facial muscles ? 

 In such a question, however, a 

 trustworthy decision can of 

 course only be arrived at after 

 extended comparative inquiry." 

 In addition to the facial 

 region, there are three others 

 in which progressive muscular 

 variations are to be found. 

 Taking first the hand, we may 

 select for special consideration 

 the thujmb. We are immedi- 

 ately struck by its apparent 

 superfluity of muscles. 1 Our 

 attention is specially arrested 

 by the long flexor of the thumb 



1 For instance, the abductor pollicis 

 has often a double or even triple 

 tendon, and supernumerary tendons of 

 the most various muscles, as if attracted 

 by a magnet, often become inserted into 

 the thumb (e.g. tendons from the 

 brachio radialis, extensor pollicis longus 

 and brevis, extensor longus radialis and 

 extensor digitorum communis). In all 

 these we probably have to do with the 

 beginnings of secondary processes of 

 differentiation, which have already been 

 indicated in connection with the skeleton 

 of the hand (ante, p. 77). 



