118 
Fic. 75.—DEEP DorsaAL MUSCLES OF THE 
FOREARM. One-fifth natural size. (After 
Rauber. ) , 
hu, humerus; w/., olecranon process of ulna; 
rd., radius; pr., processus styloideus 
ulne ; mc., os metacarpeum secundum. 
a. M. anconeus; f.p., M. flexor pro- 
fundus digitorum; fic, flexor carpi 
ulnaris, separated from the fascia of the 
forearm; ¢.., extensor carpi radialis 
brevior ; e./., the tendon of the extensor 
carpi radialis longior; e.p’., M. ext. 
metacarpi pollicis ossis; ej”. M. ext. 
primi internodii pollicis; e.p”’., M. ext. 
secundi internodii pollicis; e.7., M. ext. 
indicis ; ¢.m., insertion of the extensor 
tendon into the middle finger, and its 
connection with the second and third 
dorsal interossei. 
fingers. 
THE STRUCTURE OF MAN 
We saw above that a num- 
ber of muscles and tendons 
meet in the thumb; and the 
same applies, though to a lesser 
degree, to the great toe. To it 
offshoots of the extensor hallucis 
longior and the tibialis anticus 
or their tendons pass; these, 
however, do not indicate the 
commencement of a new de- 
velopment, but rather a rever- 
sion to a former condition, in 
which the great toe was capable 
of freer movement. | 
It would be difficult to 
decide to what extent the 
variations which occur on the 
ulnar border of the forearm 
and hand, in the region of the 
extensor and flexor carpi ulnaris 
and the extensor digiti quinti 
proprius, may be the beginnings 
of a progressive development. 
On the other hand, there can 
be no doubt that the changes 
at the fibular border of the 
foot, which have already been 
mentioned (ante, p. 112), are 
degenerations. 
The already described dif- 
ferentiation of a flexor longus 
pollicis and a_ flexor longus 
hallucis out of the original 
simple flexor masses, finds a 
parallel in the Ontogeny and 
Phylogeny of the superficial 
and deep common flexors of the 
The two latter are 
connected by an interchange of 
fibres which may amount to 
complete fusion; and in many 
of the lower Vertebrates these muscles may not only be con- 
