+80 The Phylogeny of the Palmar Musculature 
On the radial side the flexor brevis superficialis is somewhat more 
strongly represented than on the ulnar. The large muscle mass which 
forms the thenar eminence may be regarded as consisting of three 
portions, recognizable both in dissections and sections: (1) a portion 
formed by a band (Fig. 6, abp) which arises from the dorsal surface 
of the crescentic sesamoid cartilage of the radial side of the wrist (s), 
(2) a larger and broader portion arising from the volar surface of the 
annular hgament, its origin extending ulnarly to the lne of the pro- 
fundus tendon for the index and (3) a portion (Fig. 7, fbp,.) which 
arises from the radial side of the sheath for the long flexor tendons 
Fic. 7. Transverse section through the hand of the opossum. ad*~*, adductors of 
the second and fourth digits; adm, adductor minimi digiti; adp, adductor pollicis; 
fb‘, flexor brevis pollicis; fobp,, and fbp,, radial and ulnar slips of the flexores 
breves profundi; im, intermetacarpales; 7, lumbricales; m, median nerve; p, 
tendons of the flexor profundus digitorum; s, tendons of the flexor sublimis digi- 
torum; ws, superficial branch of the ulnar nerve; x, remnants of the flexor brevis 
superficialis. 
and is in contact by its volar edge with the second portion just men- 
tioned but distinguishable from it in transverse sections by. the greater 
obliquity at which it is cut at its origin. This third portion does not 
concern us now, since there is reason to suppose that it is a portion 
of a deeper layer and therefore belongs to a different group of muscles 
than the other two which, it may be remarked, insert into the outer 
surface of the base of the proximal phalanx of the thumb. The first 
portion seems to be entitled to the name abductor pollicis applied to it 
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