MUSCLES OF THE ARM. 
319 
its natural separation into two parts, which represent the persistent middle and inferior elements. 
The commonest variety is one im which the more superficial (inferior) part of the muscle extends 
come connected with a strong tendon, 
further down the arm than usual, so as to be in- 
serted into the internal intermuscular septum, 
or even into the internal condyle of the 
humerus. A third slip (coraco-brachialis 
superior or brevis, rotator humeri) may more 
rarely be present, forming a short muscle aris- 
ing from the root of the coracoid process, and 
inserted into the inner side of the humerus 
just below the capsule of the shoulder joint. 
The biceps (in. biceps brachii) is the 
large superficial muscle which lies on 
the front of the upper arm. It arises 
by two heads. (1) The short head (caput 
breve) is attached in common with the 
coraco-brachialis to the tip of the cora- 
coid process of the scapula. This head 
forms a separate fleshy belly, which is 
united to the long head by an invest- 
ment of the deep fascia. (2) The long 
head (caput longum) arises by a round 
tendon from the supra-glenoid impres- 
sion at the root of the coracoid process 
and from the glenoid ligament on either 
side. Its tendon traverses the cavity of 
the shoulder joint, and emerging from 
the capsule (invested by a prolongation 
of the synovial membrane), it occupies 
the bicipital groove of the humerus, 
covered by a fascial prolongation of the 
tendon of the pectoralis major. In the 
upper arm it forms a fleshy belly united 
to that derived from the short head by 
an envelope of deep fascia. 
The insertion of the muscle is lke- 
wise twofold. (1) The two bellies be- 
attached deeply in the hollow of the 
elbow to the rough posterior portion of 
the bicipital tubercle of the radius. A 
bursa separates the tendon from the 
anterior portion of the tubercle. (2) 
From the inner and anterior part of 
the tendon, and partly in continuity 
with the fleshy fibres of the muscle, a 
strong membranous band (the semilunar 
or. bicipital fascia) extends downwards 
and inwards over the hollow of the elbow 
to join the deep fascia covering the 
origins of the flexor and pronator muscles 
of the forearm. 
__ Except at its origin and insertion 
the biceps muscle is placed superficially 
on the front of the arm, concealing the 
brachialis anticusand musculo-cutaneous 
nerve. The brachial artery and median 
nerve lie along its inner border. 
cover of the deltoid and pectoralis major. 
the elbow hes beneath the end of the brachial and the beginning of the radial artery. 
— DELTOID 
=~ _——— INFRASPINATUS 
——__TERES MAJOR 
— LATISsImMuS 
DORSI 
BRACHIALIS ANTICUS 
TRICEPS 
External intermuscular septum 
BRACHIO-RADIALIS 
Ulnar nerve 
Mi) EXTENSOR CARPI RADIALIS 
LONGIOR 
ANCONEUS 
EXTENSOR CARPI RADIALIS 
BREVIOR 
Deep fascia of forearm 
EXTENSOR COMMUNIS DIGITORUM 
EXTENSOR CARPI ULNARIS 
— EXTENSOR OSSIS METACARPI 
POLLICIS 
] __-— EXTENSOR BREVIS POLLICIS 
EXTENSOR MINIMI DIGITI 
TENDONS OF EXTENSORS OF 
CARPUS 
Posterior annular ligament 
EXTENSOR LONGUS POLLICIS 
EXTENSOR INDICIS 
Fic. 237.—THE MUSCLES ON THE BACK OF THE 
ARM, FOREARM, AND HAND. 
The origin of the muscle is deeply placed under 
The tendon of insertion in the hollow of 
