116 
Fig. 73.—Drep MuscLes ON THE FLEXOR 
SIDE OF THE ForREARM. 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 
ulne; /.0., the orbicular ligament ; p.s’., 
proc. styloideus radii; p.s"., proc. sty- 
loideus ulne; e.c., eminentia carpi ul- 
naris ; /.c., lig. accessorium cubiti mediale; 
s.. M. supinator; 7/., M. flexor longus 
pollicis; j.y.,°M. flexor protumadlnis 
digitorum ; p.g., M. pronator quadratus ; 
f.b. deep head of the flexor brevis 
pollicis ; a.p., M. adductor pollicis ; 7.p., 
M. interosseus dorsalis primus; 7.d., Mm. 
interossei dorsales et volares; Oc., 
bicipital tendon. 
THE STRUCTURE OF MAN 
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 thumb. We are immedi- 
ately struck by its apparent 
superfluity of muscles! 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 (eg. 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). 
