D. J. (Daniel John) Cunningham.

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Ligamentum carpi dorsale



Sheath of extensor digiti quinti
M. abductor digiti quinti



Tendon of extensor digitorum /'

communis
Tendon of extensor indicis U




FIG. 76. Dissection of the Back of the Forearm, Wrist, and Hand,
showing Mucous Sheaths of Tendons.

Dissection. Remove the thin deep fascia of the dorsum of
the hand, clear away the mucous sheaths of the tendons and
clean the tendons, but do not injure (i) the dorsal carpal liga-
ment, (2) the blood-vessels which lie deep to and in the intervals
between the tendons, (3) the slips which connect the tendon to
the ring finger with that on each side of it. Three tendons must
VOL. I 12



178 THE SUPERIOR EXTREMITY

be followed to the thumb, that of the abductor pollicis longus
to the base of the metacarpal bone, that of the extensor pollicis
brevis to the base of the first phalanx, and the tendon of the
extensor pollicis longus to the base of the terminal phalanx.

There are four tendons of the extensor digitorum communis,
one for each finger. Each of the four expands, on the dorsum
of the first phalanx of the finger to which it belongs, into an
extensor expansion which covers the whole of the dorsum of the
phalanx.

Near the distal extremity of the first phalanx the extensor
expansion divides into three pieces, an intermediate piece and
two collateral pieces. The weaker intermediate piece is inserted
into the base of the second phalanx. The lateral pieces unite
with one another on the dorsum of the second phalanx before
they are inserted into the base of the terminal phalanx. Care-
fully define this arrangement on at least one finger. The
tendon of the extensor indicis passes along the ulnar side of the
tendon of the extensor digitorum communis to join the extensor
expansion of the index finger, and the two tendons of the extensor
digiti quinti join the extensor expansion of the little finger.

Clean the margins of the extensor expansion of one or more
fingers, and pass the handle of a scalpel between the expansion
and the middle of the first phalanx, then note, as the expansion
is put on the stretch, that, just beyond the metacarpo-phalangeal
joint, the expansion is joined, on each side, by structures which
pass to it through the interosseous spaces. On the radial side
it is joined by the tendon of a lumbrical muscle and by a slip
from the tendon of an interosseous muscle, and, on the ulnar
sides, by a slip from a tendon of an interosseous muscle, except
in the case of the little finger where there is, of course, no inter-
osseous muscle on the ulnar side. The dissector will have no
difficulty in displaying the association ot the lumbrical muscles
with the extensor expansions at the present stage of the dis-
section. The connections of the interossei cannot be properly
demonstrated until a later stage.

The Extensor Expansions on the Fingers. The dissector
who has carefully followed the above instructions will have
recognised that by means of the extensor expansions a
common extensor tendon, a lumbrical, and one or more inter-
ossei gain insertion into the dorsal aspects of the bases of
the second and terminal phalanges of each finger, and
through the same medium the second and terminal phalanges
of the index and little fingers are attached to the special
extensors of those digits. The dissector should now note
the movements he can make with his own fingers : (i) by use
of the flexor muscles alone he can flex all three joints of the
fingers, the metacarpo-phalangeal, and the proximal and distal
interphalangeal joints; (2) by use of the extensor muscles alone
he can extend all three joints ; (3) by use of the flexors and
extensors simultaneously he can flex the interphalangeal and



FOREARM AND HAND



179



extend the metacarpo-phalangeal joints ; (4) he can also flex
the metacarpo-phalangeal joints and extend the interphalangeal
joints. The last combination of movements is called " putting
the fingers in the writing position." It is due mainly to the
actions of the lumbricals and interossei, which pass from the
volar to the dorsal aspect across the metacarpo-phalangeal
joints, and so are enabled to flex those joints, whilst by virtue
of their attachments to the extensor expansions they can
extend the interphalangeal joints.



Os triquetrum
Os pisiforme



Os lunatum

Os capitatum



Os hamatum



Extensor carpi ulnaris




|Os naviculare manus
Extensor carpi radialis brevis
/ Os multangulum minus

} Os multangulum majus

Extensor carpi radialis longus
Abductor pollicis longus



FIG. 77. Dorsal aspect of the Bones of the Carpus and Metacarpus,
with Muscular Attachments mapped out.

M. Extensor Carpi Radialis Longus. The long radial
extensor of the carpus is placed dorsal to the brachio-radialis.
It arises from the dista third of the lateral epicondylic ridge
of the humerus, and from the lateral intermuscular septum.
From the fleshy portion of the muscle a long tendon pro-
ceeds, which passes under cover of the dorsal carpal ligament,
and is inserted into the dorsal aspect of the base of the
metacarpal bone of the index finger. The muscle is supplied
by a branch of the trunk of the radial nerve (O.T. musculo-
spiral) which enters it proximal to the elbow. The long

I 12 a



i8o THE SUPERIOR EXTREMITY

radial extensor of the wrist helps to extend and abduct the
hand at the wrist-joint, and it assists in flexion of the elbow
(Figs. 74, 75, 76).

M. Extensor Carpi Radialis Brevis. The extensor carpi
radialis brevis is closely associated with the preceding muscle.
It arises, by the common extensor tendon, from the lateral
epicondyle of the humerus ; it derives fibres also from the
radial collateral ligament of the elbow-joint, from the in-
vesting deep fascia, and the fibrous septa in connection
with it. The tendon of the muscle accompanies that of
the long radial extensor under cover of the dorsal carpal
ligament, and is inserted into the dorsal aspect of the base
of the third metacarpal bone, immediately beyond the root
of its styloid process. This muscle is supplied by the deep
branch of the radial nerve by a twig given off before the nerve
pierces the supinator muscle. It is an extensor of the wrist
and the elbow, and an abductor of the hand at the wrist-joint.

M. Extensor Digitorum Communis. The extensor digi-
torum communis takes origin, by the common tendon,
from the lateral epicondyle of the humerus. The deep
fascia and the intermuscular septa in relation to it also
contribute fibres. Its fleshy belly, in the distal part of the
forearm, ends in four tendons, which pass under cover of
the dorsal carpal ligament. On the dorsum of the hand
they diverge and proceed onwards to the four fingers. Their
arrangement and attachments on the dorsum of the hand and
fingers have already been considered (p. 177). The muscle is
supplied by the dorsal interosseous nerve. It is an extensor of
all the joints of the fingers, of the wrist, and of the elbow.

M. Extensor Digit! Quinti Proprius (O.T. Extensor
Minimi Digiti). The extensor digiti quinti proprius is a
slender fleshy belly which at first sight appears to be a part of
the preceding muscle, but its tendon passes through a special
compartment in the dorsal carpal ligament. It arises in
common with the extensor digitorum communis. Its tendon
of insertion splits into two parts. The lateral of the two
joins the tendon of the extensor digitorum communis, which
passes to the little finger, and the medial part ends in the
extensor expansion on the dorsum of the first phalanx of the
little finger. The muscle is supplied by the dorsal interosseous
nerve. It is an extensor of all the joints of the little finger,
and it aids in extension of the wrist and elbow.



FOREARM AND HAND 181

M. Extensor Carpi Ulnaris. The extensor carpi ulnaris
arises, by means of the common extensor tendon, from
the lateral epicondyle of the humerus ; from the fascia
of the forearm, and from the intermuscular septum between
it and the extensor digiti quinti proprius. In the middle
third of the forearm it receives some fibres from the strong
fascial layer which binds it to the dorsal border of the
ulna. The tendon does not become free from the fleshy
fibres until it approaches close to the wrist. It occupies
the groove on the dorsal aspect of the distal end of the
ulna, between the head and styloid process, and, passing
under cover of the dorsal carpal ligament, is inserted into the
tubercle on the base of the metacarpal bone of the little
finger. The muscle is supplied by the dorsal interosseous
nerve. It is an extensor of the wrist and elbow, and it takes
part in the movement of adduction at the wrist, when it acts
simultaneously with the flexor carpi ulnaris.

M. Anconaeus. The anconaeus lies at the lateral part of
the dorsal aspect of the elbow joint. It is a small, short
muscle, of triangular outline, which arises, by a relatively
small origin, from the back of the lateral epicondyle of the
humerus. The insertion is into the lateral border of the
olecranon of the ulna and the proximal third of the dorsal
surface of the body of the ulna. The nerve of supply has
already been dissected. It is a long slender branch which is
given off from the trunk of the radial nerve, behind the
middle third of the humerus, and it descends through the
substance of the medial head of the triceps before it reaches
the anconaeus. In addition, the distal part of the muscle
sometimes receives a branch from the dorsal interosseous
nerve. It is an extensor of the elbow joint.

Dissection. To expose the deep muscles of the back of the
forearm and the dorsal interosseous vessels and nerve the
extensor digitorum communis and the extensor digiti quinti
must be reflected. Divide the fleshy portion of each, about the
middle of its length, and turn the proximal parts of the divided
muscles towards their origins and the distal parts towards the
insertions. As the muscles are reflected care must be taken to
secure and preserve the twigs from the dorsal interosseous nerve
which enter their deep surfaces. When the reflection is com-
pleted pull aside the extensor carpi ulnaris ; then the greater
parts of the dorsal interosseous vessels and nerve and the deep
muscles of the forearm will be exposed. The muscles which
are exposed are, from above downwards, the supinator, the
abductor pollicis longus, the extensor pollicis brevis, and the
i 12 &



1 82 THE SUPERIOR EXTREMITY

extensor indicis. The dorsal interosseous nerve appears through
the substance of the supinator, crosses the surface of the
abductor pollicis longus, and dips deep to the 1 extensor pollicis
longus. The dorsal interosseous artery appears between the
adjacent borders of the supinator and the abductor pollicis
longus and descends along the radial border of the extensor
carpi ulnaris superficial to the extensor pollicis longus and the
extensor indicis. First clean the dorsal ( interosseous nerve and
secure its branches. After it pierces the supinator it gives
branches of supply to all the deep muscles except the supinator,
and to three of the superficial muscles, viz., the extensor
digitorum communis, the extensor digiti quinti, and the extensor
carpi ulnaris. The branches to the superficial muscles were
found as the extensor digitorum communis and the extensor
digiti quinti were reflected. The branch to the extensor indicis
is given off before the nerve dips deep to the extensor pollicis
longus, and it crosses the superficial surface of the long
extensor of the thumb. When it has been found pull the
extensor pollicis longus and the extensor indicis towards the
medial side, and follow the dorsal interosseous nerve, which
passes deep to both of them, to the back of the radius where it
enters the osteo-fascial compartment through which the extensor
digitorum communis and the extensor indicis pass to the dorsum
of the hand. Where it lies under cover of the extensor pollicis
longus it is joined by the perforating branch of the volar inter-
osseous artery, which pierces the interosseous membrane about
50 mm. above the wrist, and then accompanies the dorsal
interosseous nerve. Pull aside the tendons of the extensor
communis and the extensor indicis beyond the dorsal carpal
ligament and find the terminal part of the nerve and the con-
tinuation of the artery, deep to the tendons on the back of the
wrist joint. The nerve ends in a gangliform enlargement from
which twigs are distributed to the ligaments of the wrist joint,
and the volar interosseous artery terminates by joining the
dorsal carpal arterial arch.

Now clean the deep muscles, note the osteo-fascial compart-
ments on the back of the radius through which they pass to the
hand, and trace their tendons to their insertions.

Deep Muscles. These are (i) the supinator; (2) the
abductor pollicis longus ; (3) the extensor pollicis brevis ; (4)
the extensor pollicis longus ; and (5) the extensor indicis
proprius (Fig. 79).

The supinator will be recognised from the close manner
in which it is applied to the proximal part of the body of
the radius. The other muscles take origin proximo-distally
in the order in which they have been named. The attach-
ments of the supinator cannot be satisfactorily studied at
present. They will be described at a later stage of the
dissection.

M. Abductor Pollicis Longus (O.T. Extensor Ossis
Metacarpi Pollicis). The long abductor of the thumb arises



FOREARM AND HAND 183

from both bones of the forearm, and from the interosseous
membrane, which stretches between them. Its origin from
the radius corresponds to the middle third of the dorsal
surface of that bone j its origin from the ulna is more proximal,
from the lateral part of the dorsal surface of the body, im-
mediately distal to the oblique line which marks the distal
limit of the insertion of the anconseus. The muscle proceeds
distally and laterally, and comes to the surface in the interval
between the extensor digitorum communis and the extensor
carpi radialis brevis. Then it crosses the two radial extensors,
closely accompanied by the extensor pollicis brevis. The
tendon which issues from it, as it becomes superficial, is
continued distally, over the lateral side of the expanded
distal end of the radius, and under cover of the dorsal carpal
ligament, and is inserted into the lateral side of the base of
the metacarpal bone of the thumb. The muscle is supplied
by the dorsal interosseous nerve. In addition to being an
abductor of the thumb it assists in producing supination and
abduction of the hand (Figs. 74, 75, 76, 79).

M. Extensor Pollicis Brevis (O.T. Extensor Primi Inter-
nodii Pollicis). The short extensor of the thumb is placed
along the distal border of the preceding muscle. It arises
from a small portion of the dorsal surface of the radius, and
also from the interosseous membrane. Its tendon is closely
applied to that of the abductor pollicis longus, and accom-
panies it deep to the dorsal carpal ligament. It must be
traced, on the dorsal aspect of the metacarpal bone of the
thumb, to the base of the proximal phalanx, into which it is
inserted. The muscle is supplied by the dorsal interosseous
nerve. It is an extensor of the first interphalangeal joint
and of the metacarpo-phalangeal joint of the thumb, and it
takes a subsidiary part in the production of abduction of
the hand.

M. Extensor Pollicis Longus (O.T. Extensor Secundi Inter-
nodii Pollicis). The long extensor of the thumb takes origin
from the lateral part of the dorsal surface of the body of the
ulna, in its middle third, and also from the interosseous
membrane. It overlaps, to some extent, the preceding
muscle, and it ends in a tendon which passes under cover
of the dorsal carpal ligament, where it occupies a deep narrow
groove on the dorsum of the distal end of the radius.
On the carpus it takes an oblique course, and, after crossing

i 12 c



184



THE SUPERIOR EXTREMITY



" M. triceps brachii



M. flex,
carp. uln.



M. ext.
carp. uln. '



M. pronator
teres



the tendons of the two radial extensors and the radial artery,

it reaches the
thumb. It is
inserted into
the base of the
distal phalanx
of the thumb
and is supplied
by a branch of
the dorsal inter-

M. biceps brachii osseous nerVe .

M. supinator 1^-^^ y \ \ \\ It is an extensor

of all the joints
of the thumb,
and it takes
part in the in-
itiation of sup-
ination of the
forearm (Figs.
78, 74, 75, 76,
79).

When the
thumb is power-
fully extended, in
the living person,
the tendons of its
three last - men-
tioned muscles be-
come prominent
on the lateral
aspect of the wrist.
The oblique course
of the tendon of
the extensor pol-
licis longus is
rendered evident,
and a distinct de-
pression between
it and the other
two tendons is
seen.



Ext. carp,
uln.




Rad. extensors
Abd. poll. long,
and ext. poll,
brev.



Ext. dig. comm. and ext.
indicis proprius



Ext



long>



M. Extensor
Indicis Pro-
prius. The

special extensor of the index finger arises, distal to the pre-



FIG. 78. Dorsal aspect of the Bones of the Forearm,
with Attachments of Muscles mapped out.



FOREARM AND HAND 185

ceding muscle, from a limited area on the dorsal surface of
the ulna and from the adjacent part of the interosseous
membrane. Its tendon accompanies the tendons of the
extensor digitorum communis through the most medial
groove on the back of the radius, under cover of the dorsal
carpal ligament, and is enclosed in the same mucous sheath.
On the dorsum of the hand it lies along the medial side of
the most lateral tendon of the common extensor, and it
terminates in the expansion of that tendon on the dorsum
of the first phalanx of the index finger. It is supplied by
a branch of the dorsal interosseous nerve. It is an extensor
of all the joints of the index finger, and it takes part in the
production of extension of the wrist joint.

Arteria Interossea Dorsalis. The dorsal interosseous
artery arises, in the front part of the forearm, from the
common interosseous branch of the ulnar artery. It at
once proceeds dorsally, between the two bones of the
forearm, in the interval between the oblique cord and the
proximal border of the interosseous membrane. It appears
in the back of the forearm between the contiguous borders
of the supinator and the abductor pollicis longus, and
then it extends distally between the superficial and deep
muscles on the dorsum of the forearm. It gives branches
to the adjacent muscles, and before it reaches the distal end
of the forearm it is greatly reduced in size. In a well-
injected limb it will be seen to end on the dorsum of the
carpus by anastomosing with the volar interosseous artery
and the dorsal carpal arteries. In addition to the branches
which it supplies to the muscles, it gives off one large branch
called the interosseous recurrent artery (Fig. 79).

The arteria interossea recurrens takes origin from the parent
trunk as it appears between the supinator and the abductor
pollicis longus, and turns proximally, under cover of the
anconceus muscle, to reach the dorsal aspect of the lateral
epicondyle of the humerus.

Nervus Interosseus Dorsalis. The dorsal interosseous
nerve is the continuation of the deep terminal branch of the
radial (musculo-spiral) nerve. It reaches the dorsum of the
forearm by traversing the substance of the supinator, and at
the same time winding round the lateral aspect of the body
of the radius. It emerges from the supinator a short distance
proximal to the distal border of the muscle, and passes



i86



THE SUPERIOR EXTREMITY



M. triceps brachii



Annular ligament of the ^Qs
radius

Dorsal interosseous nerve
M. anconaeus -

Interosseous recurrent

M. pronator teres .||

Nerve to ext. pollicis

longus and ext. indicis

proprius

Dorsal interosseous nerve"



M. extensor indicis proprius ,3



Extensor digiti quinti proprius
Extensor digitorum communis _

Dorsal carpal artery _
Radial artery ^




M. biceps brachii
M. brachialis



* M. abductor pollicis longus



M. extensor pollicis brevis



FIG. 79. Dissection of the Dorsum of the Forearm and Hand.



FOREARM AND HAND



187



interosseous nerve, it
gives branches both to
the supinator and to
the extensor carpi
radialis brevis. After
forearm, as the dorsal



Brachial artery



Profunda artery of
the arm



Superior ulnar
collateral artery



distally between the superficial and deep muscles on the
back of the forearm. At the proximal border of the extensor
pollicis longus, it leaves the dorsal interosseous artery, dips
anterior to the extensor pollicis longus, and joins the per-
forating branch of the
volar interosseous
artery on the dorsal
aspect of the interosse-
ous membrane. Ac-
companied by that
artery it descends,
through the most medial
groove on the back of
the radius with the ten-
dons of the extensor
digitorum communis
and the extensor indicis
proprius, to the back of
the wrist where it ends
in a gangliform enlarge-
ment which lies between
the extensor tendons
and the posterior liga-
ment of the wrist.

The branches which
spring from the dorsal
interosseous nerve in
the forearm are given
entirely to muscles.
Before the deep branch
of the radial nerve
pierces the supinator
and becomes the dorsal




Inferior ulnar
collateral artery



Ant. terminal
branch of profunda
artery



Radial artery

Ulnar artery

.., Ulnar recurrent
'-' arteries

Interosseous recurrent artery
_ Dorsal interosseous artery
-Volar interosseous artery

FIG. 80. Diagram of Anastomosis around
the Elbow Joint.



it appears on the dorsum of the
interosseous nerve, it supplies the
extensor digitorum communis, the extensor digiti quinti pro-
prius, the extensor carpi ulnaris, the abductor pollicis longus,
two extensors of the thumb, and the extensor indicis proprius.



1 88 THE SUPERIOR EXTREMITY

It supplies, therefore, all the muscles on the lateral and
dorsal aspects of the forearm, with the exception of the
brachio-radialis and the extensor carpi radialis longus, which
derive their nerve-supply directly from the radial nerve (O.T.
musculo-spirat}. The anconseus derives its main nerve of supply
from the radial nerve, but not infrequently it also obtains a
second twig from the dorsal interosseous nerve.

Dissection. Detach the anconaeus from its origin and throw
it towards its insertion in order to display the course of the
dorsal interosseous recurrent artery. Trace that artery to the
back of the lateral epicondyle, and then examine the arterial
anastomosis around the elbow- joint.

Anastomosis around the Elbow Joint. The series of
inosculations around the elbow should now be reviewed as a
whole. A distinct inosculation will be found to take place
upon both the anterior and posterior aspect of each epi-
condyle of the humerus. Behind the lateral epicondyle the
interosseous recurrent artery joins the posterior branch of the
profunda brachii artery: anterior to the same epicondyle the
anterior branch of the profunda brachii artery communicates
with the radial recurrent On the medial side of the joint the
anterior and posterior ulnar recurrent arteries ascend respectively
in front of and behind the medial epicondyle ; the former
anastomoses with the anterior branch of the inferior ulnar
collateral artery^ and the latter with the posterior branch of
the same artery and with the superior ulnar collateral artery,

In this account of the anastomosis around the elbow joint
only the leading inosculations are mentioned. Rich net-
works of fine vessels are formed over the olecranon and the
two epicondyles of the humerus. One very distinct and fairly
constant arch requires special mention. It is formed by a
branch which crosses the posterior aspect of the humerus,
immediately proximal to the olecranon fossa, and connects
the posterior branch of the profunda brachii artery with
the posterior branch of the inferior ulnar collateral artery.

Terminal Branch of the Arteria Interossea Volaris.
The so-called perforating branch of the volar interosseous
artery is a vessel of some size, and is, really, the main con-
tinuation of the artery. It perforates the interosseous mem-
brane about 50 mm. proximal to the distal end of the radius,
and is at once joined by the dorsal interosseous nerve. It
descends, with the nerve, in the most medial groove on the



FOREARM AND HAND 189

dorsum of the distal end of the radius, to the dorsum of the
carpus, where it anastomoses with the end of the dorsal inter-
osseous artery and terminates in the dorsal carpal arterial



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