302 MUSCLES AND FASCIAE. 



interposed between it and the Teres minor and Infra-spinatus ; the fibres are 

 directed upwards and outwards, and terminate in a flat tendon, ahout two inches 

 in length, which is inserted into the posterior bicipital ridge of the humerus. The 

 tendon of this muscle, at its insertion into the humerus, lies behind that of the 

 Latissimus dorsi, from which it is separated by a synovial bursa. 



Relations. By its posterior surface, with the integument, from which it is 

 separated, internally, by the Latissimus .dorsi ; and externally, by the long head of 

 the Triceps. By its anterior surface, with the Subscapularis, Latissimus dorsi, 

 Coraco-brachialis, short head of the Bi<?eps, the axillary vessels, and brachial 

 plexus of nerves. Its upper border is at first in relation with the Teres minor, 

 from which it is afterwards separated by the long head of the Triceps. Its 

 lower border forms, in conjunction with the Latissimus dorsi, part of the posterior 

 boundary of the axilla. 



Nerves. The Supra-spinati and Infra-spinati muscles are supplied by the supra- 

 scapular nerve ; the Teres minor, by the circumflex ; and the Teres major, by the 

 subscapular. 



Actions. The Supra-spinatus assists the Deltoid in raising the arm from the 

 side ; its action must, however, be very feeble, from the very disadvantageous 

 manner in which the force is applied. The Infra-spinatus and Teres minor rotate 

 the head of the humerus outwards ; when the arm is raised, they assist in retaining 

 it in that position, and carrying it backwards. One of the most important uses 

 of these three muscles is the great protection they afford to the shoulder-joint, the 

 Supra-spinatus supporting it above, and preventing displacement of the head of 

 the humerus upwards, whilst the Infra-spinatus and Teres minor protect it behind, 

 and prevent dislocation baclovards. The Teres major assists the Latissimus dorsi 

 in drawing the humerus downwards and backwards when previously raised, and 

 rotating it inwards ; when the arm is fixed, it may assist the Pectoral and Latis- 

 simus dorsi muscles in drawing the trunk forwards. 



ANTERIOR HUMERAL REGION. 

 Coraco-brachialis. Biceps. Brachialis Anticus. 



Dissection. The arm being placed on the table, with the front surface uppermost, make a 

 vertical incision through the integument along the middle line, from the middle of the interval 

 between the folds of the axilla, to about two inches below the elbow-joint, where it should be 

 joined by a transverse incision, extending from the inner to the outer side of the forearm ; the 

 two flaps being reflected on either side, the fascia should be examined. 



The deep fascia of the arm, continuous with that covering the shoulder and 

 front of the great Pectoral muscle, is attached, above, to the clavicle, acromion> 

 and spine of the scapula ; it forms a thin, loose, membranous sheath investing the 

 muscles of the arm, sending down septa between them, and composed of fibres 

 disposed in a circular or spiral direction, these being connected together by 

 vertical fibres. It differs in thickness at different parts, being thin over the Biceps, 

 but thicker where it covers the Triceps, and over the condyles of the humerus ; 

 and is strengthened by fibrous aponeuroses, derived from the Pectoralis major and 

 Latissimus dorsi, on the inner side ; and from the Deltoid, externally. On either 

 side it gives off a strong intermuscular septum, which is attached to the condyloid 

 ridge and condyle of the humerus. These septa serve to separate the muscles of 

 the anterior from those of the posterior brachial region. The external inter- 

 muscular septum extends from the lower part of the anterior bicipital ridge, along 

 the external condyloid ridge, to the outer condyle ; it is blended with the tendon 

 of the Deltoid, gives attachment to the Triceps behind, to the Brachialis anticus, 

 Supinator longus, and Extensor carpi radialis longior, in front, and is perforated 

 by the musculo-spiral nerve, and superior profunda artery. The internal inter- 

 muscular septum, thicker than the preceding, extends from the lower part of the 

 posterior bicipital ridge below the Teres major, along the internal condyloid 

 ridge to the inner condyle ; it is blended with the tendon of the Coraco-brachialis* 



