A. BETWEEN THE TENDONS.--=Mm. lumbricales= (Fig. 88, _f_, _f′_).--Four
small muscles in the palm of the hand.
_Origin_ by fleshy fibres from the outer (palmar) surface of the tendon
common to the ulnar four parts of the profundus (_c′_).
_Insertion_ (_f′_).--The four slips are flat at their origin. Each
becomes cylindrical and curves about the base of one of the four ulnar
digits and is inserted into the radial side of the base of the first
phalanx close to its ventral border.
[Illustration: FIG. 89.--DEEP MUSCLES OF THE PALM OF THE HAND.
_a_, M. flexor brevis pollicis; _b_, M. adductor pollicis; _c_, M.
interosseus of second digit (M. flexor brevis digiti secundi); _d_, M.
adductor digiti secundi; _e_, M. interosseus of third digit; _f_, M.
interosseus of fourth digit; _g_, M. opponens digiti quinti; _h_, M.
interosseus of fifth digit (M. flexor brevis digiti quinti); _i_, M.
abductor digiti quinti. 1-5, the digits in order.]
_Action._--Bend the digits toward the radial side.
B. MUSCLES OF THE THUMB.--=M. abductor brevis pollicis= (Fig. 77, _w_)
(includes also the opponens pollicis of man).--A very minute, probably
rudimentary muscle.
_Origin_ from the transverse ligament (1) which connects the prominent
fibrous, hairless projection that lies over the pisiform bone with the
radial border of the head of the radius. The muscle passes radiodistad
and ends in a very slender tendon, the insertion of which is into the
base of the first phalanx of the thumb.
=M. flexor brevis pollicis= (Fig. 89, _a_).
_Origin_ by fleshy fibres from the adjacent borders of the os magnum and
scapholunar bones and from the fascia which bridges the intervening
groove for the flexor carpi radialis.
_Insertion_ by a short tendon into the base of the first phalanx of the
pollex.
_Action._--Flexor of the thumb.
=M. adductor pollicis= (Fig. 89, _b_).
_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, _h_)
which is continued dorsad to join the extensor tendon of the digit.
D. SPECIAL MUSCLES OF THE SECOND 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, _d_).
_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. abductor digiti quinti=
(Fig. 89, _i_).--A thick, small, conical bundle.
_Origin_ from the distal surface of the pisiform bone and from the
transverse ligament on the ulnar side of the pisiform. It ends in a
slender tendon which runs along the ulnar side of the fifth metacarpal
to its
_Insertion_ into the ulnar side of the base of the first phalanx of the
fifth digit.
=M. flexor brevis digiti quinti= (Fig. 89, _h_; Fig. 88, _e_).--This
covers the ventral surface of the fifth metacarpal, and is really the
interosseus of this digit.
_Origin_ by fleshy fibres from the ventral surface of the base of the
fifth metacarpal; from the ventral process of the unciform bone, and
from the transverse ligament proximad of the fifth metacarpal.
_Insertion_ by fleshy fibres into the ventral border of the proximal end
of the first phalanx of the fifth digit.
=M. opponens (adductor) digiti quinti= (Fig. 89, _g_).
_Origin_ by a flat tendon from the ventral surface of the os magnum on
the ulnar side of the adductor pollicis (_b_). It passes toward the
ulnar side and distad, the fibres diverging to their
_Insertion_ (1) into nearly the whole of the radial surface of the fifth
metacarpal, (2) into the base of its first phalanx.