188 The Phylogeny of the Forearm Flexors 
anconeus, also arising from the condyle of the humerus and inserting 
into the olecranon process. 
Upon the radial side there is a 
flexor carpi radialis (F.C.R.), 
extending from the internal con- 
dyle to the base of one or more 
of the radial metacarpals, and a 
pronator radii teres, again from 
the condyle and inserting a vary- 
ing distance down the outer sur- 
face of the radius. 
The median portion of the 
arm is occupied by (1) a palmaris 
longus (P.L.), extending from 
the internal condyle to the pal- 
mar aponeurosis, and (2) a large 
mass, composed of several more or 
less distinct portions and which 
Fra.4. Transverse section through the fore- May be termed the flexor com- 
arm of an hypothetical mammal. ai, anterior : = ue c 
interosseus nerve; C, centralis; F.C. R., flexor munis digitorum. ‘The  consti- 
carpi radialis; F. C. U. and F.C. U.2, lateral 5 : 
and medial portions of the flexor carpi ul tution of this muscle has been 
naris; m, median nerve; PL, palmaris longus; 5 5 — 
PQ, pronator quadratus; PT, pronator teres; admirably elucidated by Windle 
R, radius; Ra, radialis; RC, condylo-radialis ; 5 
U.ulna; wu, ulna nerve; UC, condylo-ulnaris; (1890), and I propose to follow 
Ul, ulnaris. c Bone ; 
closely his description of it, based 
as it is upon a profound and critical analysis of its various components. 
My observations have confirmed his for the most part, the only modifi- 
eation which I shall make being the omission for the present of a sub- 
limis component. I do this because, as I hope to show later, the sublimis 
is far from being an equivalent muscle throughout the mammalian series, 
a view which differs fundamentally from that apparently held by Windle. 
Omitting the sublimis, then, as a distinct component, there are 
recognizable in the flexor communis digitorum five components. Three 
of these, named by Windle, the condylo-radialis (Fig. 4, R. C.), the 
condylo-ulnaris (U.C.) and the centralis (C.), have their origin from 
the internal condyle of the humerus; the fourth and fifth components, 
the radialis (Ra) and the ulnaris (Ul), on the other hand arise from 
the bones from which they derive their names. All the five components 
unite in a common tendon. 
Finally, as one of the mammalian muscles there is to be mentioned 
the pronator quadratus, which extends across between the distal two- 
