MUSCLES OF THE THORACIC LIMBS. 185 
M. adductor pollicis (Fig. 89, 4). 
Origin by fleshy fibres from the ventral border of the os 
magnum. It curves about the base of the first metacarpal on 
its ulnar side to its insertion. 
Insertion by fleshy fibres into the base of the first phalanx 
of the pollex on its ulnar side. 
C. MuscLes LYING BETWEEN THE METACARPALS.— 
Mm. interossei (Fig. 89).—Small stout muscles lying on the 
palmar surfaces of the metacarpals of the second, third, fourth, 
and fifth digits. 
Origin by fleshy fibres from the ventral or lateral surfaces 
of the bases of the metacarpals. Near the distal end of the 
metacarpal each divides into two masses which pass onto the 
lateral surfaces of the metacarpal, so as to leave the ventral 
surface of the distal end exposed. 
Insertion partly onto the lateral surfaces of the base of the 
first phalanx and its sesamoids, and partly by a slender tendon 
(Fig. 84, #) which is continued dorsad to join the extensor 
tendon of the digit. 
D. SPECIAL MUSCLES OF THE SEGOND DIGIT (THE 
INDEX).—M. flexor brevis digiti secundi (or indicis).—This 
name may be applied to M. interosseus of the second digit 
(Fig. 89, c). 
M. abductor digiti secundi.—This name might be applied 
to a portion of the interosseus of the second digit which is 
sometimes differentiated from the remainder. 
Origin from the radial and ventral surfaces of the base of 
the second metacarpal, and from the ventral surface of the 
trapezium. 
Insertion into the radial side of the base of the first phalanx 
of the second digit and into its sesamoid. 
M. adductor digiti secundi (Fig. 89, 2). 
Origin from the ventral surface of the os magnum. 
Insertion into the ulnar side of the base of the first phalanx 
of the second digit. ; 
E. SPECIAL MUSCLES OF THE FIFTH DIGIT.—M. ab- 
ductor digiti quinti (Fig. 89, z).—A thick, small, conical 
bundle. 
