Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Todd, Robert Bentley
arm, muscles of the. 
arm the median nerve crosses the artery in 
general superficial to it, but sometimes under¬ 
neath it, while in the lower part of the arm this 
nerve is invariably on its inner side. 
When called upon to expose the brachial 
artery for the purpose of tying it, the surgeon 
should recollect that the course of the artery 
may be readily determined by a line drawn 
from the coracoid process to a point midway 
between the condyles of the humerus on the 
anterior surface of the elbow; hence his in¬ 
cision for the purpose of exposing the brachial 
artery should be always made along the course 
of this line and perpendicular to the axis of 
the os humeri. (See Brachial Artery.) 
For Bibliography, see Anatomy (Intro¬ 
(John Hart.) 
cles which clothe the os humeri are part of the 
deltoid, the biceps, coruco-brachialis, brachiœus 
anticus, the origin of the supinator lougus in 
front, and the triceps behind. 
The deltoid belongs to the shoulder, and 
will be described with the other muscles of 
that part. (See Scapular Region.) 
1. Coraco-brachialis (coraco-humeral).— 
The coraco-brachialis arises from the point 
of the coracoid process, in common with the 
short head of the biceps, tendinous in front and 
fleshy behind ; it separates from the biceps at 
its middle third, passes inwards, and is in¬ 
serted tendinous into the internal surface of the 
humerus a little above its middle between the 
triceps and brachiæus anticus. 
This muscle has in front of it the deltoid 
aud pectoralis major, which cover and conceal 
from view its upper part; behind it the tendon 
of the subseapularis, the tendons of the latissi- 
mus dorsi and teres major, the axillary artery, 
the median and the external cutaneous nerves. 
The latter nerve perforates the muscle about 
its middle, and passes through its substance 
to reach the outer side of the arm ; hence the 
epithet perforatus has been applied to this 
muscle. The coraco-brachialis can carry the 
arm forwards and inwards ; when the humerus 
is fixed, it can act upon the scapula, and by 
depressing its coracoid angle, elevate the in¬ 
ferior angle and separate it from the ribs. 
2. Biceps flexor cubiti ( scapulo-coraco-ra- 
dial).—This is a long muscle swollen in the 
centre, divided above into two portions called 
heads, one internal short, the other external 
long. The internal or short head arises from 
the coracoid process of the scapula in common 
with the coraco-brachialis. The long head is 
attached by a long slender flattened tendon to 
the upper part of the margin of the glenoid 
cavity, and is united by a dense cellular tissue 
to the glenoid ligament. This tendon passes 
over the head of the humerus, and enters 
the groove between the two tuberosities in 
which it is bound down by the fibres of the 
capsular ligament of the shoulder-joint ; a pro¬ 
longation of the synovial membrane also lines 
the groove, and forms a synovial sheath for 
the tendon ; the tendon terminates in a fleshy 
belly which unites with the short head to form 
the large belly of the biceps ; the muscle ter 
minâtes below in a tendon, which, passing 
over the brachiæus anticus and the front 
of the elbow-joint, sinks into a triangular 
hollow between the pronator teres and supina¬ 
tor longus to be inserted into the back part 
of the tubercle of the radius ; but before it sinks 
into this triangular space, it sends off from its 
internal side an aponeurosis (the semilunar 
fascia of the biceps), which is inserted into the 
internal condyle, and the fascia which covers the 
muscle at the inner side of the bend of the elbow. 
The biceps is covered by the deltoid, the 
pectoralis major, the fascia of the arm and 
integuments in front ; behind it lies on the 
humerus, coraco-brachialis, brachiæus anticus, 
and the external cutaneous nerve ; internal to 
it lie the coraco-brachialis and brachial artery. 
It bends the elbow and makes tense the fascia 
of the fore-arm ; it is also a very powerful 
supinator of the hand by virtue of its insertion 
into the radius. If the fore-arm be extended and 
fixed, it will depress the scapula on the humerus. 
3. Brachiœus anticus ( B. internus, hume- 
rocubital).—When the biceps has been raised 
from its situation, we observe the brachiæus 
anticus deeply situated on the front of the arm ; 
it arises by two fleshy tongues, one on each 
side of the insertion of the deltoid ; from the 
whole of the anterior surface of the humerus, 
and the internal intermuscular ligament which 
separates it from the triceps, its fleshy fibres 
pass downwards in front of the elbow, and 
end in a broad tendon which is inserted into a 
triangular roughness on the anterior surface 
of the coronoid process of the ulna. This 
muscle is covered in front by the biceps, supi¬ 
nator longus, the fascia of the arm and integu¬ 
ments, the musculo-cutaneous and median 
nerves, the brachial artery, and the pronator 
teres; behind it covers the front of the lower 
part of the humerus and the elbow-joint. This 
muscle is the most powerful flexor of the fore¬ 
arm upon the arm. As Bichat remarks, flexion 
of the fore-arm takes place directly if the bra¬ 
chiæus combines its action with that of the 
biceps ; if either acts alone, the flexion is in the 
direction inwards or outwards; inwards when the 
biceps acts alone, outwards when the brachiæus. 
4. Triceps extensor cubiti (brachiœus posti¬ 
cus, tri-scapulo-humero-olecranien.)—The tri¬ 
ceps muscle of the arm is situated on the poste¬ 
rior surface of the humerus, and, as its name 
implies, has its origin by three heads. The long 
head arises by a short, flat, thick tendon from 
a rough portion of the inferior costa of the 
scapula, immediately below the glenoid cavity, 
and passing downwards in front of the inser¬ 
tion of the teres minor, and behind the teres 
major it forms a large belly, which covers the 
posterior surface of the os humeri. The se¬ 
cond or short head arises from the outer and 
back part of the os humeri, beginning by a 
pointed origin immediately below the insertion 
of the teres minor ; it continues to arise from 
the external ridge of the humerus as low down 
as the external condyle ; from the surface of 
the bone behind this ridge, and from the back 
part of the external intermuscular ligament. 
The third head, which is the shortest, called


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