M. clavobrachialis and the pectoralis group (Fig. 65, page 109) lie
partly in this region; they have been described.
=M. coracobrachialis= (Fig. 77, _f_; Fig. 79, _c_).--A very short muscle
covering the inner (medial) surface of the capsule of the
shoulder-joint. It extends from the coracoid process to the proximal end
of the humerus.
_Origin_ (Fig. 78, _h_).--By a round tendon from the tip of the coracoid
process.
_Insertion_ (Fig. 82, _e_) usually by fleshy fibres on an area five to
eight millimeters long and about half as wide, which lies on the medial
side of the humerus parallel with the ridge which runs from the dorsal
end of the lesser tuberosity to the shaft and close to it. The proximal
end of the area is about one centimeter from the proximal end of the
head of the humerus.
_Relations._--Medial surface with the biceps (Fig. 77, _g_), pectoralis
minor (Fig. 65, _o_), and teres major (Fig. 77, _c_). Lateral surface
with the capsule of the shoulder-joint. Dorsal border with the
subscapularis (Fig. 77, _a_) and the long portion of the caput mediale
of the triceps (Fig. 77, _j_).
_Action._--Adducts the humerus.
The part of the coracobrachialis just described is known as the _short_
head. A _long_ head is sometimes found. It is a conical bundle of
fibres of varying size, which arises from the tendon of origin of the
short head. It passes distad into a long and extremely slender tendon,
the insertion of which varies greatly in different individuals. It is
commonly on the humerus in the region of the supracondyloid foramen.
=M. epitrochlearis= or extensor antibrachii longus (Fig. 65, _r_).--A
thin, flat muscle on the inner or medial side of the brachium, from the
lateral surface of the latissimus dorsi (Fig. 65, _q_) to the olecranon
process of the ulna.
_Origin_ from the lateral or outer surface of the ventral border of the
latissimus dorsi (Fig. 65, _q_) near the insertion of the cutaneus
maximus. Fibres are often attached to the teres major and the pectoralis
minor.
_Insertion_ by a flat tendon which is closely connected with that of the
pectoantibrachialis (Fig. 65, _m_) and is continuous with the general
antibrachial fascia, into the caudal border of the cutaneous (dorsal)
surface of the olecranon process of the ulna.
_Relations._--Outer (medial) surface with the integument, the latissimus
dorsi (Fig. 65, _q_), and the cutaneus maximus. Inner (lateral) surface
with the biceps (Fig. 65, _t_), caput longum (Fig. 65, _s_), and caput
mediale (Fig. 77, _j_, _k_) of the triceps.
_Action._--Extends the antibrachium and tends to supinate the hand by
rotating the ulna.
=M. biceps brachii= (Fig. 77, _g_; Fig. 65, _t_).--A thick, fusiform
muscle lying on the front (ventral) surface of the humerus.
_Origin_ (Fig. 76, _c_) by a strong, round tendon from the bicipital
tubercle of the glenoid angle of the scapula, at its coracoid margin.
(In man there is a second head--coracoid head--from the coracoid
process.) The tendon passes through the capsule of the joint and then
along the bicipital groove, which is converted into a canal by a strong
ligament.
_Insertion_ by a rounded tendon (Fig. 87, _b_) on the bicipital
tuberosity of the radius (Fig. 86, _k_).
_Relations._--The tendon of origin passes through the capsule of the
joint, which is covered by a part of the pectoralis minor. The muscle is
then spanned for the middle part of its course by the bicipital arch
(Fig. 65, _t′_), a description of which is given below. Farther distad
it is covered by the clavobrachial (Fig. 65, _k_) and epitrochlearis
(Fig. 65, _r_). At its distal end (Fig. 79, _l′_) the muscle passes
between the pronator teres on the radial side and the conjoined tendon
of the brachialis and clavobrachial (Fig. 79, _i′_) on the other. The
biceps lies throughout most of its length on the ventral surface of the
humerus, and touches along the medial border of its inner surface the
coracobrachialis (Fig. 77, _f_), the teres major, (Fig. 77, _c_), the
intermediate portion of the caput mediale of the triceps (Fig. 77, _k_),
and the short portion (Fig. 77, _l_) of the same. Its lateral border
touches the pectoralis minor (Fig. 65, _o_) and the brachialis (Fig. 79,
_i_).
_Action._--Flexes the forearm, and tends to supinate the hand.
=The bicipital arch= (Fig. 65, _t′_) is a tendinous arch formed over the
biceps muscle. Its outer or lateral pillar is formed by the tendon of
the pectoralis minor (_o_), to which may be added part of the latissimus
(_q_) tendon. Its inner or medial pillar is formed by the conjoined
tendon of the teres major and latissimus dorsi (Fig. 79, _d′_), while
the xiphihumeralis (Fig. 65, _p_), cutaneus maximus (Fig. 62, _b_), and
epitrochlearis (Fig. 65, _r_) are connected with one or the other pillar
or with the muscles composing them. The caudal portion of the deep layer
of the pectoralis major (Fig. 65, _l_) may be connected with the inner
pillar.
=M. brachialis= (Fig. 79, _i_; Fig. 75, _i_).--From the lateral surface
of the humerus to the ulna.
_Origin_ (Fig. 83, _g_, _g′_) from a long V-shaped line two to four
millimeters wide on the lateral surface of the humerus. The apex of the
V is just distad of the teres minor tubercle (_d_). Its dorsal limb
(_g′_) extends along the lateral supracondyloid ridge to a point
opposite the proximal margin of the supracondyloid foramen; its ventral
limb (_g_) extends in the direction of the deltoid ridge to the middle
of the bone. No muscle-fibres take origin between the two limbs. The
fibres converge and end in a flat tendon which joins the tendon of the
clavobrachial (Fig. 79, _k_).
_Insertion_ (Fig. 87, _c_).--The dorsal portion of the depressed rough
area on the lateral surface of the ulna just distad of the semilunar
notch.
_Relations._--Outer surface with the acromiodeltoid (Fig. 75, _f_), the
caput laterale of the triceps (Fig. 75, _h_), the brachioradialis (Fig.
75, _k_), and the proximal end of the extensor carpi radialis longus
(Fig. 75, _l_). Inner surface with the humerus. Medial edge with the
pectoralis major (Fig. 65, _l_) and the biceps (Fig. 77, _g_).
_Action._--Flexor of the antibrachium.
=M. triceps brachii.=--The triceps muscle of the cat, like that of man,
is divisible (as its name indicates) into three main portions. These are
a lateral portion (caput laterale), an intermediate or long portion
(caput longum), and a medial portion (caput mediale). The first two
correspond to the similarly named heads in man; the medial portion falls
into a number of subdivisions whose homologues are uncertain.
[Illustration: FIG. 79.--DEEP MUSCLES ON THE MEDIAL SIDE OF THE
HUMERUS.
_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
coracobrachialis; _d_, M. teres major (_d′_, its tendon); _e_, part of
M. latissimus dorsi joining the teres major; _f_, cut end of M.
pectoralis minor; _g_, long part of caput mediale of M. triceps
brachii; _h_, intermediate part of caput mediale of M. triceps; _i_,
M. brachialis (_i′_, its tendon); _j_, short part of caput mediale of
M. triceps; _k_, cut end of M. clavobrachialis; _l_, _l′_, cut ends of
M. biceps; _m_, M. brachioradialis; _n_, M. extensor carpi radialis
longus; _o_, M. extensor carpi radialis brevis; _p_, fifth head of M.
flexor profundus digitorum; _q_, first head of M. flexor profundus
digitorum. 1, humerus; 2, olecranon; 3, medial epicondyle of humerus.]
=Caput laterale= (anconeus lateralis) (Fig. 75, _h_; Fig. 68, _l_).--The
lateral portion is a flat muscle (most of it subcutaneous) on the
lateral side of the brachium, connecting the proximal end of the humerus
with the olecranon process of the ulna.
_Origin_ (Fig. 81, _h′_).--By a flat tendon from the proximal portion of
the deltoid ridge and the distal border of the teres minor tubercle.
_Insertion_ (Fig. 86, _c_) by a thin, flat tendon into the lateral
border of the dorsal surface of the ulna between a point opposite the
distal margin of the semilunar notch and the proximal end of the
olecranon.
_Relations._--Lateral surface with the integument, and at the proximal
end with the spinodeltoid and acromiodeltoid (Fig. 75, _e_ and _f_).
Medial surface with the brachialis (Fig. 75, _i_), the caput longum
(_g_), the caput mediale, the brachioradialis (_k_), the anconeus (Fig.
80, _l_), and the origins of the extensor carpi radialis longus (Fig.
75, _l_), the extensor communis digitorum (_m_), and the extensor
digitorum lateralis (_n_).
=Caput longum= (anconeus longus) (Fig. 75, _g_; Fig. 68, _k_; Fig. 77,
_i_).--A prismatic, fusiform mass connecting the scapula with the
olecranon.
_Origin_ (Fig. 78, _i_) by a thick, flat tendon from a triangular area
one or two centimeters long at the glenoid end of the scapula on the
glenoid border. The base of the area is about one millimeter from the
margin of the glenoid fossa.
_Insertion_ (Fig. 86, _b_).--The muscle ends in a thick tendon which
passes over the bifurcated ventral end of the olecranon and is inserted
upon the rounded tuberosity which forms the dorsal angle of the
olecranon.
_Relations._--Lateral surface with the caput laterale (Fig. 75, _h_), a
portion of the caput mediale (Fig. 77, _j_ and _k_), the spinodeltoid
(Fig. 75, _e_), the infraspinatus (Fig. 75, _c_), and the integument.
Medial surface with the epitrochlearis (Fig. 65, _r_) and the conjoined
portions of the latissimus dorsi and teres major (Fig. 79, _d′_).
Ventral border with the caput mediale (Fig. 77, _j_ and _k_).
=Caput mediale.=--The medial head consists of three portions (Fig. 79,
_g_, _h_, _j_).
(1) The long portion (anconeus posterior) (Fig. 77, _j_; Fig. 79, _g_;
Fig. 80, _f_).
_Origin_ (Fig. 83, _e_) from a triangular area on the dorsal surface of
the humeral shaft. The base of the area is against the articular head,
and its apex about one-sixth the length of the humerus from the head. It
is between the coracobrachialis and the lateral head of the triceps.
[Illustration: FIG. 80.--DEEP MUSCLES ON THE LATERAL SURFACE OF THE
HUMERUS.
_a_, part of M. supraspinatus; _b_, part of M. infraspinatus; _c_, M.
teres minor; _d_, M. teres major; _e_, part of M. latissimus dorsi
joining M. teres major; _f_, long part of caput mediale of M. triceps
brachii; _g_, cut insertion of M. acromiodeltoideus; _h_, M.
brachialis; _i_, M. brachioradialis; _j_, intermediate part of caput
mediale of M. triceps brachii; _k_, M. extensor carpi radialis longus;
_l_, M. anconeus; _m_, M. extensor communis digitorum. 1, great
tuberosity of humerus; 2, 3, superficial radial and dorsal
interosseous branches, respectively, of the radial nerve.]
_Insertion_ (Fig. 86, _a_).--The muscle ends in a long, slender tendon
which passes through the furrow on the ventral angle of the olecranon
and is inserted into an oblique ridge which forms the dorsal limit of
the furrow. The tendon is separated from the floor of the furrow by a
synovial bursa.
(2) The intermediate portion (anconeus internus) (Fig. 77, _k_; Fig. 79,
_h_; Fig. 80, _j_).
_Origin_ (Fig. 82, _g_) by fleshy fibres from a triangular area proximad
of the middle of the dorsomedial surface of the humerus. The length of
the area equals about one-fourth the length of the bone. Its apex points
proximad and is almost continuous with the apex of the area of origin of
the long portion.
_Insertion_ (Fig. 87, _i_) by short tendon-fibres into the medial border
of the ventral and proximal surfaces of the olecranon. It is connected
with the tendon of the long portion.
(3) Short portion (Fig. 79, _j_; Fig. 77, _l_).
_Origin_ (Fig. 82, _h_) from the outer surface of the bony bar which
encloses the supracondyloid foramen of the humerus, as far as the medial
epicondyle.
_Insertion_ (Fig. 87, _e_) by fleshy fibres into the medial border of
the olecranon distad of the tuberosity for the insertion of the caput
longum.
_Relations_ of the caput mediale.--Lateral surface with the caput
laterale (Fig. 75, _h_), the humerus, and the anconeus (Fig. 80, _l_).
Dorsal surface with the caput longum (Fig. 77, _i_), the epitrochlearis
(Fig. 65, _r_), and the teres major (Fig. 79, _d_). Ventral surface with
the biceps (Fig. 77, _g_).
_Action of the Triceps._--The entire triceps group forms a powerful
extensor of the forearm. The short portion of the medial head tends also
to rotate the arm outward, so as to supinate the hand.
=M. anconeus= (Fig. 80, _l_).--A triangular muscle on the outside of the
elbow-joint from the humerus to the ulna.
_Origin_ (Fig. 83, _i_).--An irregularly triangular area at the distal
end of the dorsal surface of the humerus. The area of origin is limited
laterally by the sharp lateral supracondyloid ridge. It sometimes
extends onto the lateral epicondyle.
[Illustration: FIG. 81.--VENTRAL SURFACE OF HUMERUS, WITH THE AREAS OF
ATTACHMENT OF MUSCLES.
FIG. 82.--MEDIAL SIDE OF HUMERUS, WITH THE AREAS OF ATTACHMENT OF
MUSCLES.
FIG. 83.--DORSAL SURFACE OF THE LEFT HUMERUS, WITH THE AREAS OF
ATTACHMENT OF MUSCLES.
Fig. 81.--_a_, M. subscapularis; _b_, M. supraspinatus; _c_, Mm. teres
major and latissimus dorsi; _d_, M. pectoralis minor; _e_, deep layer
of M. pectoralis major; _f_, superficial layer of M. pectoralis major;
_g_, M. acromiodeltoideus; _h_, M. spinodeltoideus; _h′_, caput
laterale of M. triceps; _i_, M. brachialis; _j_, second portion of M.
brachialis; _k_, M. extensor carpi radialis longus; _l_, M. extensor
carpi radialis brevis; _m._ M. extensor communis digitorum; _n_, M.
extensor lateralis digitorum; _o_, M. extensor carpi ulnaris; _p_,
short portion of caput mediale of M. triceps; _q_, M. pronator teres;
_r_, M. palmaris longus; _s_, third and fourth parts of M. flexor
profundus digitorum; _t_, M. flexor carpi radialis; _u_, second head
of M. flexor profundus digitorum.
Fig. 82.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
pectoralis minor; _d_, long portion of caput mediale of M. triceps;
_e_, M. coracobrachialis; _f_, Mm. teres major and latissimus dorsi;
_g_, intermediate portion of caput mediale of M. triceps; _h_, deep
layer of M. pectoralis major; _i_, superficial layer of M. pectoralis
major; _j_, M. anconeus; _k_, short portion of caput mediale of M.
triceps; _l_, M. pronator teres; _m_, M. flexor carpi radialis; _n_,
second head of M. flexor profundus digitorum; _o_, third and fourth
heads of M. flexor profundus digitorum; _p_, M. palmaris longus; _q_,
M. flexor carpi ulnaris.
Fig. 83.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
infraspinatus; _d_, M. teres minor; _e_, long portion of caput mediale
of M. triceps; _f_, M. coracobrachialis; _g_, _g′_, M. brachialis;
_h_, intermediate portion of caput mediale of M. triceps; _i_, M.
anconeus; _j_, short portion of medial head of M. triceps; _k_, M.
pronator teres; _l_, second and third heads of M. flexor profundus
digitorum; _m_, M. palmaris longus; _n_, M. extensor carpi ulnaris.]
_Insertion_ (Fig. 86, _d_).--The lateral surface of the ulna from the
distal margin of the semilunar notch to the proximal end of the
olecranon. The muscle covers the capsule of the joint and is closely
adherent to it.
_Relations._--Outer (dorsal) surface with the caput laterale (Fig. 75,
_h_) and the intermediate portion (Fig. 80, _j_) of the caput mediale.
Inner surface with the bones and the capsule of the joint.
_Action._--Keeps the capsule tense and probably rotates the ulna
slightly so as to pronate the hand.