ANTERIOR HUMERAL REGION. 



207 



the pectoralis major, tendon of the supra-spinatus, infra-spinatus, 

 teres minor, teres major, scapular and external head of the triceps, 

 the circumflex vessels anterior and posterior, and humerus. By its 

 anterior border with the external border of the pectoralis major, 

 from which it is separated by a cellular interspace, lodging the 

 cephalic vein and descending branch of the thoracico-acromialis 

 artery. Its posterior border is thin above, where it is connected with 

 the aponeurotic covering of the infra-spinatus muscle, and thick below. 

 Actions. The deltoid is the elevator muscle of the arm in a direct 

 line, and by means of its extensive origin can carry the arm forwards 

 or backwards so as to range with the hand a considerable segment 

 of a large circle. The arm, raised by the deltoid, is a good illus- 

 tration of a lever of the third power, so common in the animal ma- 

 chine, by which velocity is gained at the expense of power. In this 

 lever, the weight (hand) is at one extremity, the fulcrum (the glenoid 

 cavity) at the opposite end, and the power (the insertion of the mus- 

 cle) between the two, but nearer to the fulcrum than to the weight. 



Anteri9r Humeral Region. 

 Crac*-brachialis, 



Fig. 82 * 



Braehialis antiews. 



Dissection. These muscles are exposed, 

 on the removal of the integument and fascia 

 from the anterior half of the upper arm, and 

 clearing away the cellular tissue. 



The Coraco-brachialis, a name composed 

 of its points of origin and insertion, arises 

 from the coracoid process in common with 

 the short head of the biceps; and is inserted 

 into a rough line on the inner side of the 

 middle of the humerus. 



Relations. By its anterior surface with 

 the deltoid, and pectoralis major. By its 

 posterior surface with the shoulder joint, the 

 humerus, subscapularis, teres major, latissi- 

 mus dorsi, short head of the triceps, and an- 

 terior circumflex vessels. By its internal 

 border with the axillary and brachial vessels 

 and nerves, particularly with the median and 

 external cutaneous nerve, by the latter of 

 which it is pierced. By the external border 

 with the short head of the biceps and bra- 

 chialis anticus. 



The Biceps (bis xs<paXa, two heads) arises 



* The muscles of the anterior aspect of the upper arm. 1. The coracoid process of 

 the scapula. 2. The coraco-clavicular ligament (trapezoid), passing upwards to the 

 scapular end of the clavicle. 3. The cotaco-acrom-al ligament, passing outwards to the 

 acromion. 4. The subscapularis muscle. 5. The teres major. 6. The coraco-bra- 

 chiahs. 7. The biceps. 8. The upper end of the radius. 9. The brachialis anticus. 

 10. The internal head of the triceps. 





