380 MUSCLES AND FASCIAE. 



its upper border, with the Infraspinatus. By its lower border, with the Teres 

 Major, from which it is separated anteriorly by the long head of the Triceps. 



The Teres Major is a broad and somewhat flattened muscle, which arises from 

 the dorsal aspect of the inferior angle of the scapula, and from the fibrous septa 

 interposed between it and the Teres Minor and Infraspinatus ; the fibres are 

 directed upwards and outwards, and terminate in a flat tendon about 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 Biceps, 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 pos- 

 terior boundary of the axilla. 



Nerves. The Supraspinatus and Infraspinatus muscles are supplied by the 

 suprascapular nerve; the Teres Minor by the circumflex, and the Teres Major 

 by the subscapular. 



Actions. The Supraspinatus assists the Deltoid in raising the arm from the 

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

 manner in which the force is applied. The Infraspinatus 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 Supraspinatus supporting it above, and preventing displace- 

 ment of the head of the humerus upwards, whilst the Infraspinatus and Teres 

 Minor protect it behind, and prevent dislocation backwards. 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 Latissimus Dorsi muscles in drawing the trunk forwards. 



ANTERIOR HUMERAL EEGIOIST. (Fig. 237.) 

 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, and connected together by ver- 

 tical 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; 

 it 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 intermuscular 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 Lon- 

 gior in front; and is perforated by the musculo-spiral nerve, and superior pro- 



