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- 

 DUCTION.) 



(John Hart.) 



ARM, MUSCLES OF THE. The mus- 

 cles which clothe the os humeri are part of the 

 deltoid, the biceps, coraco-brachiulis, brachiaus 

 anticus, the origin of the supinator longus 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 . Coruco-brachiulis (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 brachiaeus anticus. 



This muscle has in front of it the deltoid 

 and pectoralis major, which cover and conceal 

 from view its upper part; behind it the tendon 

 of the subscapularis, 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 Jlexor cubiti (scapulo-coraco-ra- 

 d'utl). 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 tubevosities 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 



219 



the large belly of the biceps ; the muscle ter 

 minates below in a tendon, which, passing 

 over the brachiaeus 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, brachiaeus 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 thescapulaon the humerus. 



3. Brachitsus anticus ( B. internus, hume- 

 rocubital). When the biceps has been raised 

 from its situation, we observe the brachiaeus 

 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- 

 chiaeus combines its action with that of the 

 biceps ; if either acts alone, the flexion is in the 

 directioninwardsoroutwards; inwards when the 

 biceps acts alone, outwards when the brachiaeus. 



4. Triceps extensor cubiti (brachiaus 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 



