_Fascia of the Forearm._--The muscles of the forearm are not in contact
with the skin, but are covered by the strong =antibrachial fascia=. This
consists of two layers. The =superficial= one is a continuation of the
general subcutaneous fascia of the arm; it covers the forearm as a
continuous sheet which becomes thinner distad, and is finally lost near
the wrist. The =deep= layer forms a dense, tendinous sheet which is
closely applied to the muscles. It begins partly as a continuation of
the general fascia of the arm, partly from the tendons of the triceps
and epitrochlearis muscles. The sheet is attached to the dorsal surface
of the ulna, between the extensor carpi ulnaris and the first head of
the flexor profundus digitorum. It surrounds the forearm as a continuous
sheath. On the lateral surface it dips between the extensor muscles,
becoming closely attached to them and forming a partial sheath for each;
it is attached with special firmness to their tendons. On the medial
side of the arm the fascia passes smoothly over the flexors without
dipping between them; it is continuous, however, with the border of the
pronator teres, and distad of this muscle it is firmly attached to the
radius.
At the wrist the fascia becomes attached to the longitudinal ridges on
the dorsal surface of the head of the radius, bridging thus the
intervening grooves and holding the tendons in place between the ridges.
The fascia then continues to form the dorsal fascia of the hand. On the
ventral side of the wrist the fascia becomes thickened to form a strong
=transverse ligament= (Fig. 77, 1), which is attached at its radial and
ulnar ends to the carpus, and which holds in place the tendons of the
flexor muscles. Distad of the transverse ligament the fascia spreads out
in the palm of the hand, and becomes united with the fibrous pad which
is situated here. On the fingers the fascia becomes attached to the
phalanges, forming tendinous sheaths, the so-called =vaginal ligaments=,
for the flexor muscles. Near the base and the head of the first phalanx
strong, narrow, ring-like bands, the =annular ligaments= (Fig. 88, 2),
are formed in these sheaths; these surround and bind down the tendons of
the flexor muscles.
A. MUSCLES ON THE ULNAR AND DORSAL SIDE OF THE FOREARM (extensors and
supinators) (Fig. 75, p. 158).
=M. brachioradialis= or supinator longus (Fig. 75, _k_; Fig. 77,
_n_).--This is a ribbon-like muscle lying on the lateral side of the
brachium and the ventrolateral border of the antibrachium just beneath
the superficial fascia. It connects the humerus and the radius.
_Origin._--By a thin tendon from about the middle fifth of the dorsal
border of the humerus, or sometimes proximad of the middle. The muscle
curves over the outer surface of the brachialis (Fig. 75, _i_), to which
it is closely applied, and runs along the lateral border of the
antibrachium to its insertion.
_Insertion_ by a short tendon into the ridge which forms the ventral
limit of the groove on the outer surface of the styloid process of the
radius and upon the adjacent ligaments.
_Relations._--Outer surface with the integument, and at the proximal end
with the caput laterale of the triceps (Fig. 75, _h_). Inner surface
with the brachialis (_i_), the extensor carpi radialis longus (_l_) and
brevis, and the extensor communis digitorum (_m_).
_Action._--Supinator of the hand.
=M. extensor carpi radialis longus= (Fig. 75, _l_; Fig. 77, _o_).--This
lies along the radial side of the forearm, and connects the humerus and
the second metacarpal.
_Origin_ (Fig. 81, _k_) from the middle portion of the lateral
supracondyloid ridge between the origin of the brachialis (_j_) and the
anconeus. About the middle of the forearm the muscle ends in a slender
tendon (Fig. 84, _e_) which passes through the groove on the radial side
of the dorsal surface of the distal end of the radius.
_Insertion_ (Fig. 84, _c_).--The tendon passes across the carpus and is
inserted onto the dorsal surface of the base of the second metacarpal on
the radial side just distad of the groove for the radial artery.
_Relations._--Outer surface at the proximal end with the caput laterale
of the triceps (Fig. 75, _h_), farther distad with the integument and
the brachioradialis (_k_); the distal tendon with the extensor pollicis
brevis (Fig. 84, _d_). Radial surface with the brachialis (Fig. 75, _i_)
and the integument. Ulnar surface with the extensor carpi radialis
brevis (Fig. 77, _p_), and near the proximal end with the extensor
communis digitorum (Fig. 75, _m_).
_Action._--Extensor of the hand.
=M. extensor carpi radialis brevis= (Fig. 77, _p_).--A slender muscle
from the humerus to the third metacarpal.
_Origin_ (Fig. 81, _l_) from the distal part of the lateral
supracondyloid ridge distad of the extensor longus. Near the carpus the
muscle ends in a slender tendon which passes through the groove with the
extensor longus tendon. The tendon then diverges from the extensor
longus and has its
_Insertion_ (Fig. 84, _f_) into the radial side of the dorsal surface of
the base of the third metacarpal.
_Relations._--Outer surface with the extensor longus (Fig. 77, _o_), the
integument, and distad with the extensor pollicis brevis (Fig. 84, _d_).
Radial surface with the extensor longus. Ulnar surface with the extensor
communis digitorum (Fig. 75, _m_) and the extensor brevis pollicis.
Inner surface with the pronator teres (Fig. 77, _q_), supinator (Fig.
85, _b_), and extensor brevis pollicis (Fig. 85, _a_).
_Action._--Extensor of the hand.
[Illustration: FIG. 84.--ARRANGEMENT OF THE TENDONS ON THE BACK OF THE
HAND.
_a_, M. extensor communis digitorum; _b_, M. extensor lateralis
digitorum; _c_, M. extensor indicis; _d_, M. extensor brevis pollicis;
_e_, M. extensor carpi radialis longus; _f_, M. extensor carpi
radialis brevis; _g_, M. extensor carpi ulnaris; _h_, tendons of the
interossei. 1, transverse ligament of the wrist.]
=M. extensor digitorum communis= (Fig. 75, _m_).--A slender muscle from
the lateral supracondyloid ridge of the humerus to the phalanges of the
second, third, fourth, and fifth digits.
_Origin_ (Fig. 81, _m_).--The distal surface of the lateral
supracondyloid ridge dorsad of the origin of the extensor carpi radialis
brevis.
At the junction of the middle and distal thirds of the radius the muscle
passes into a large, flat tendon (Fig. 75, _m′_) which passes through
the groove on the middle of the dorsal surface of the distal end of the
radius. The groove is converted into a canal by a strong transverse
ligament. The tendon divides near the groove into four portions (Fig.
84, _a_) which diverge and pass to the four ulnar digits.
_Insertions._--Each division of the tendon as it passes over the dorsal
surface of the first phalanx has its border connected by strong fascia
to the dorsal surface of the phalanx. It finally passes through the
groove at the distal end of the first phalanx and is inserted mostly
into the base of the second phalanx; a portion continues distad to be
inserted into the third phalanx.
_Relations._--Outer surface with the integument and at the origin with
the caput laterale (Fig. 75, _h_) of the triceps. Radial surface with
the extensor longus (_l_) and extensor brevis. Ulnar surface with the
extensor digitorum lateralis (_n_). Inner surface with the supinator
(Fig. 85, _b_) and the extensor pollicis brevis (Fig. 85, _a_).
_Action._--Extensor of the four ulnar digits.
=M. extensor digitorum lateralis= (Fig. 75, _n_). (This corresponds in
position to the extensor digiti quinti proprius of man.)
_Origin_ (Fig. 81, _n_) from the lateral supracondyloid ridge of the
humerus distad of the origin of the extensor communis.
The muscle passes along the ulnar border and dorsal surface of the
forearm between the extensor communis (Fig. 75, _m_) and the extensor
carpi ulnaris (_o_). Near the carpus it ends in a tendon (_n′_), which
divides immediately into three or four (Fig. 84, _b_). These pass
through the groove on the ulnar side of the dorsal surface of the
radius and diverge to the digits lying beneath the extensor communis
tendon.
_Insertion_ (Fig. 84, _b_).--The three tendons on the ulnar side join
the ulnar sides of the tendons of the extensor communis (_a_) at their
insertions. The radial of the four tendons (not always present) joins
the tendon of the extensor indicis (_c_) and may also give a branch to
the radial side of the base of the first phalanx of the third digit.
_Relations._--Outer surface with the integument. Radial border with the
extensor communis digitorum (_m_); ulnar border with the extensor carpi
ulnaris (_o_). Inner surface with the supinator (Fig. 85, _b_) and the
extensor brevis pollicis (Fig. 85, _a_); distad with the extensor
indicis (Fig. 85, _c_).
_Action._--Extensor of the four ulnar digits.
=M. extensor carpi ulnaris= (Fig. 75, _o_).
_Origin._--(1) By a short, broad tendon from the distal portion of the
lateral epicondyle of the humerus (Fig. 81, _o_) distad of the origin of
the extensor lateralis, and (2) by a smaller tendon from the ulna at the
dorsal tip of the semilunar notch (Fig. 86, _e_).
The muscle passes along the ulnar side of the forearm dorsad of the
extensor digitorum lateralis (_n_). It ends near the junction of the
middle and distal thirds of the forearm in a large, flat tendon (_o′_)
which is closely adherent to the ligaments of the wrist and which passes
over the distal end of the ulna to its
_Insertion_ into the tubercle on the ulnar side of the base of the fifth
metacarpal (Fig. 84, _g_).
_Relations._--Outer surface with the integument. Radial (or ventral)
border with the extensor digitorum lateralis (Fig. 75, _n_); ulnar (or
dorsal) border with the flexor profundus digitorum (_q_). Inner surface
with the radius, the extensor indicis (Fig. 85, _c_), and the extensor
pollicis brevis (Fig. 85, _a_).
_Action._--Indicated by its name.
=M. extensor indicis (proprius)= (Fig. 85, _c_; Fig. 75, _p_) (includes
extensor pollicis longus also).
_Origin_ (Fig. 86, _f_) by short, fleshy fibres from the lateral surface
of the ulna between the semilunar notch and the junction of the third
and fourth (distal) fourths.
The muscle-fibres pass obliquely distad and toward the radial side and
join the tendon (Fig. 85, _c′_), which runs nearly the whole length of
the radial surface.
_Insertion_ (Fig. 84, _c_).--The tendon passes through the groove on the
ulnar side of the dorsal surface of the base of the radius and divides
into two. Both of these usually go to the base of the second phalanx of
the second digit, but one may pass to the pollex, or there may be three
divisions going to the first three digits.
[Illustration: FIG. 85.--DEEP MUSCLES ON THE EXTENSOR SURFACE OF THE
RADIUS AND ULNA.
_a_, M. extensor brevis pollicis (_a′_, its tendon); _b_, M.
supinator; _c_, M. extensor indicis (_c′_, its tendon); _d_, tendon of
M. extensor carpi radialis brevis; _e_, tendon of M. extensor carpi
radialis longus. 1, humerus; 2, olecranon; 3, styloid process of ulna;
4, distal end of radius; 5, head of radius.]
_Relations._--Outer surface with the integument, the extensor carpi
ulnaris (Fig. 75, _o_), and the extensor digitorum lateralis (Fig. 75,
_n_). Dorsal border with the flexor profundus digitorum (Fig. 75, _q_).
Inner surface with the extensor brevis pollicis (Fig. 85, _a_).
_Action_ as indicated by the name.
=M. supinator= (Fig. 85, _b_).--A flat muscle wrapped spirally about the
proximal end of the radius.
_Origin_ by a short, strong tendon from the lateral side of the annular
ligament of the radius and by tendinous fibres from the radial
collateral ligament passing from the humerus to the radius. From the
tendon of origin the fibres diverge, passing toward the radial side and
distad.
_Insertion_ (Fig. 86, _g_).--The dorsal and part of the ventral surface
of the proximal two-fifths of the radius to within five millimeters of
the articular face of the head.
_Relations._--Outer surface with the extensor carpi radialis brevis,
extensor communis digitorum (Fig. 75, _m_), and extensor lateralis
digitorum (Fig. 75, _n_). Radial border with the pronator teres (Fig.
77, _q_). Inner surface with the radius.
_Action._--Supinator of the hand.
[Illustration: FIG. 86.--LATERAL OR EXTENSOR SURFACE OF RADIUS AND
ULNA, WITH THE AREAS OF ATTACHMENT OF MUSCLES.
_a_, long portion of caput mediale of M. triceps; _b_, caput longum of
M. triceps; _c_, caput laterale of M. triceps; _d_, M. anconeus; _e_,
M. extensor carpi ulnaris; _f_, M. extensor indicis; _g_, M.
supinator; _h_, M. extensor brevis pollicis; _i_, M. pronator teres;
_j_, M. flexor profundus digitorum; _k_, M. biceps.]
=M. extensor brevis pollicis= or extensor ossis metacarpi pollicis (Fig.
85, _a_) (includes M. abductor longus pollicis of man).
_Origin_ (Fig. 86, _h_) by fleshy fibres from the ventral half of the
lateral surface of the shaft of the ulna from the semilunar notch to the
styloid process; from the ulnar half of the dorsal surface of the radius
from the bicipital tubercle to a short distance distad of the middle of
the bone; and from the interosseous membrane between these two areas.
The fibres converge to form a strong, flat tendon (Fig. 84, _d_) which
passes obliquely over the tendons of the extensor carpi radialis longus
(_e_) and brevis (_f_) to its
_Insertion_ into the radial side of the base of the first metacarpal.
The radial sesamoid bone of the wrist is imbedded in the tendon at its
insertion.
_Relations._--Outer surface with the extensor carpi radialis brevis, the
extensor communis digitorum (Fig. 75, _m_), extensor lateralis digitorum
(Fig. 75, _n_), and extensor indicis (Fig. 85, _c_). Inner surface with
the radius and ulna, and distad with the tendons of the two extensores
carpi radiales (Fig. 84, _e_ and _f_).
_Action._--Extends and abducts the pollex.
B. MUSCLES ON THE RADIAL AND VENTRAL SIDE OF THE FOREARM (flexors and
pronators).
=M. pronator teres= (Fig. 77, _q_).
_Origin_ (Fig. 82, _l_) by a short strong tendon from the extremity of
the medial epicondyle of the humerus.
_Insertion_ (Fig. 86, _i_) by fleshy fibres and short tendinous fibres
along the medial border of the radius, at its middle. The radial edge of
the muscle is continuous with the strong deep layer of the antibrachial
fascia.
_Relations._--Outer surface with the superficial fascia. Radial border
with the tendon of the biceps (Fig. 79, _l′_), with the extensor carpi
radialis brevis (Fig. 77, _p_), and the supinator (Fig. 85, _b_). Ulnar
border with the flexor carpi radialis (Fig. 77, _r_) and part of the
flexor profundus digitorum (Fig. 77, _u_).
_Action._--Pronates the hand by rotating the radius.
=M. flexor carpi radialis= (Fig. 77, _r_).--A slender fusiform muscle.
_Origin_ (Fig. 82, _m_) from the tip of the medial epicondyle of the
humerus.
_Insertion._--The slender tendon passes through a deep groove between
the os magnum and the first metacarpal. The groove is converted into a
canal by the overlying tendons and muscles. The tendon is finally
inserted into the bases of the second and third metacarpals.
_Relations._--Outer surface with the pronator teres (Fig. 77, _q_), the
superficial fascia, and the third head of the flexor profundus (_u_).
Radial border with the pronator teres (_q_). Ulnar border with the third
and fourth heads of the flexor profundus. Inner surface with the ulna
proximad and the fifth head of the flexor profundus (_u′_) distad.
_Action_ indicated by the name.
=M. palmaris longus= (Fig. 77, _s_).--A flat fusiform muscle beneath
the fascia on the medial border of the forearm.
_Origin_ (Fig. 82, _p_) by a short flat tendon from the distal part of
the medial surface of the medial epicondyle of the humerus.
About one centimeter from the wrist the muscle ends in a flat tendon
which passes through the transverse ligament and divides on the hand
into four or five (or sometimes only three) tendons (Fig. 77, _s′_)
which diverge to the insertions. The ulnar portion of the flexor
sublimis digitorum (Fig. 77, _x_) takes origin from the common tendon
before its division.
_Insertion._--Each tendon except the first gives off a branch which
spreads out in the trilobed pad in the palm. The middle two of these may
be traced to the integument covering the pad. The tendon is then
inserted (Fig. 88, _a_) near the base of the first phalanx onto the
outer surface of the perforated portion of the flexor sublimis tendon
(_b_, _b′_) at its side, except that to the thumb, which divides near
its distal end into two which are inserted into the sesamoid bones at
the base of the first phalanx. The tendons of insertion are closely
united to the fibrous pulley-ring at the base of the first phalanx, and
each may send a slip to the base of the phalanx at either side of the
ring.
_Relations._--Outer surface with the superficial fascia and one head of
the flexor sublimis (Fig. 77, _x_). Radial border with the flexor carpi
radialis. Ulnar border with the flexor carpi ulnaris and a part of the
flexor profundus digitorum. Inner surface with the flexor carpi
radialis (_r_), the flexor carpi ulnaris (_t_), the flexor profundus
digitorum (_u_), and the radial head of the flexor sublimis digitorum.
_Action._--Flexor of the first phalanx of each of the digits.
=M. flexor carpi ulnaris= (Fig. 77, _t_, _t′_).
_Origin._--There are two heads. The first or humeral head (_t′_) takes
origin in common with the second part of the flexor profundus from the
median surface of the distal end of the humerus just distad of the
medial epicondyle (Fig. 82, _q_). The second or ulnar head (_t_) takes
origin by fleshy fibres from the lateral surface of the olecranon and
from the dorsal border of the ulna from the olecranon to a point distad
of the semilunar notch (Fig. 87, _f_). The two heads join proximad of
the middle of the forearm. The muscle passes obliquely across the
ventral surface of the forearm to its
_Insertion_ by fleshy and tendinous fibres into the proximal surface of
the pisiform bone.
_Relations._--Outer surface with the integument and the palmaris longus
(Fig. 77, _s_). Inner surface and ulnar border with the flexor profundus
digitorum.
_Action_ indicated by the name.
=M. flexor sublimis digitorum= (or perforatus).--This muscle is in two
parts, which are given a common name only because of the similar
structure and insertions of their tendons.
The =ulnar part= (Fig. 77, _x_) is a conical muscle taking origin from
the outer surface of the tendon and muscle of the palmaris longus and
from the adjacent ligament. It gives rise to two or three tendons (Fig.
88, _b_) which arise from distinct slips of the muscle; these pass to
the ulnar two or three digits. That passing to the fourth or fifth digit
receives an accessory slip from a small mass of fibres attached to the
transverse ligament on the radial side of the palmaris tendon.
The =radial part= is a small flat triangular muscle which takes origin
from the outer surface of the tendon formed by the junction of the
tendons of the first and second parts of the flexor profundus. It
divides into two slips, each giving rise to a tendon. These tendons
(Fig. 88, _b′_) pass to the second and third digits. That to the third
digit may divide into two, one of which goes to the fourth digit.
Each of the four tendons (Fig. 88, _b_ and _b′_) is perforated by a
tendon of the flexor profundus (Fig. 88, _c_) as it passes through the
fibrous pulley-ring at the base of the first phalanx. It then continues
beneath the flexor profundus tendon through the second pulley-ring (2)
and is inserted into the base of the second phalanx.
_Relations._--Outer surface of the ulnar part with the integument; inner
surface with the palmaris longus (Fig. 77, _s_). Outer surface of the
radial part with the palmaris longus; inner surface with the flexor
profundus.
_Action._--Flexor of the second phalanx of digits 2-5.
=M. flexor profundus digitorum= (or perforans).--This arises by five
heads, the tendons of which join one another at the wrist to make the
strongest and deepest of the flexor tendons.
The _first_ or _ulnar head_ has _origin_ (Fig. 87, _g_) from the dorsal
half of the medial (radial) surface of the ulna from the proximal lip of
the semilunar notch to within a centimeter of the styloid process. Its
fibres converge to a large flat tendon which forms the lateral (ulnar)
and superficial part of the common tendon.
[Illustration: FIG. 87.--RADIUS AND ULNA, Medial or Flexor Side, with
M. pronator quadratus and the Areas of Attachment of Other Muscles.
_a_, M. pronator quadratus; _b_, tendon of M. biceps; _c_, conjoined
tendon of M. brachialis and M. clavobrachialis; _d_, insertion of
caput longum of M. triceps; _e_, insertion of short portion of caput
mediale of M. triceps; _f_, origin of M. flexor carpi ulnaris; _g_,
origin of first head of M. flexor profundus digitorum; _h_, origin of
fifth head of M. flexor profundus digitorum; _i_, intermediate portion
of caput mediale of M. triceps.]
The _second head_ has _origin_ (Fig. 82, _n_) from the distal end of the
medial epicondyle of the humerus between the flexor ulnaris and the
third and fourth heads of the profundus. It may be very closely attached
to these muscles at their origins. Its tendon joins the radial border of
the tendon of the first head. From this junction the radial part of the
flexor sublimis arises.
The _third head_ (Fig. 77, _u_) has _origin_ (Fig. 82, _o_) by a strong
tendon from the medial epicondyle of the humerus, between the palmaris
(_p_) and flexor radialis (_m_). Its tendon forms the radial part of the
common tendon.
The _fourth head_ has _origin_ by a strong tendon from the medial
epicondyle of the humerus just ventrad of the origin of the second head
and the flexor ulnaris, to which many of its fibres are attached. Its
tendon forms the middle and superficial part of the common tendon.
The _fifth_ or _radial head_ (Fig. 75, _q_; Fig. 77, _u′_) has _origin_
(Fig. 87, _h_) from the middle third of the ventral surface of the shaft
of the radius over an area limited by two oblique bony ridges; from the
adjacent parts of the interosseous membrane; and from the ventral part
of the medial surface of the shaft of the ulna between a point about two
centimeters distad of the semilunar notch and the junction of the middle
and distal thirds of the shaft. Its very thick tendon forms the middle
and deep part of the common tendon.
The common tendon (Fig. 88, _c′_) covers the carpus and metacarpus
ventrally. It divides into five tendons (_c_) which pass to the five
digits and are _inserted_ into the bases of the terminal phalanges.
Those of the first four digits perforate the tendon of the flexor
sublimis (_b_) at the base of the first phalanx of each digit. At the
same place each passes through a fibrous pulley-ring attached to the
base of the phalanx. Each then passes through a second pulley-ring (2)
near the head of the phalanx and is finally inserted into the base of
the terminal phalanx.
_Relations._--Outer surface with the pronator teres (Fig. 77, _q_),
flexor carpi radialis (Fig. 77, _r_), palmaris longus (_s_), flexor
carpi ulnaris (_t_), integument, and extensor carpi ulnaris (Fig. 75,
_o_). Inner surface with the radius, ulna, interosseous membrane and
pronator quadratus (Fig. 87, _a_).
_Action._--Flexor of all the digits.
[Illustration: FIG. 88.--ARRANGEMENT OF THE TENDONS of M. palmaris
longus, M. flexor sublimis digitorum, and M. flexor profundus
digitorum, with Mm. lumbricales.
The integument, fibrous pads, and the palmaris longus (except the ends
of its tendons) have been removed; the flexor sublimis has been cut.
_a_, cut ends of tendons of M. palmaris longus; _b_, tendons of M.
flexor sublimis digitorum, ulnar division; _b′_, radial part of M.
flexor sublimis digitorum; _c_, tendons of M. flexor profundus
digitorum (_c′_, the common tendon); _d_, M. abductor digiti quinti;
_e_, M. flexor brevis digiti quinti; _f_, Mm. lumbricales (_f′_, their
tendons). 1, transverse ligament of wrist; 2, annular ligaments.]
=M. pronator quadratus= (Fig. 87, _a_).--A thick quadrangular muscle
whose fibres run obliquely between the distal ends of the ulna and
radius.
_Origin_ by fleshy fibres from about the distal half of the ventral
(flexor) surface or border of the ulna and from the interosseous
membrane adjacent to the area. The fibres pass obliquely distad toward
the radial side to their
_Insertion_ by fleshy fibres into the ventral (flexor) surface of the
radius distad of the area of origin of the fifth head of the profundus.
_Relations._--Outer surface with the flexor profundus. Inner surface
with the radius, ulna, and interosseous membrane.
_Action_ as indicated by the name.