OF THE FOREARM. 383 



muscle are directed, some downwards to the olecranon, whilst others converge 

 to the common tendon of insertion. 



The common tendon of the Triceps commences about the middle of the back 

 part of the muscle : it consists of two aponeurotic laminae, one of which is 

 subcutaneous, and covers the posterior surface of the muscle for the lower half 

 of its extent : the other is more deeply seated in the substance of the muscle ; 

 after receiving the attachment of the muscular fibres, they join together above 

 the elbow, and are inserted into the back part of the upper surface of the 

 olecranon process, a small bursa, occasionally multilocular, being interposed 

 between the tendon and the front of this surface. 



The long head of the Triceps descends between the Teres Minor and Teres 

 Major, dividing the triangular space between these two muscles and the humerus 

 into two smaller spaces, one triangular, the other quadrangular (Fig. 238). The 

 triangular space contains the dorsalis scapulae vessels ; it is bounded by the 

 Teres Minor above, the Teres Major below, and the scapular head of the Triceps 

 externally : the quadrangular space transmits the posterior circumflex vessels 

 and nerve ; it is bounded by the Teres Minor above, the Teres Major below, 

 the scapular head of the Triceps internally, and the humerus externally. 



Relations. By its posterior surface with the Deltoid above : in the rest of its 

 extent it is subcutaneous. By its anterior surface, with the humerus, musculo- 

 spiral nerve, superior profunda vessels, and back part of the elbow-joint. Its 

 middle or long head is in relation, behind, with the Deltoid and Teres Minor ; in 

 front, with the Subscapularis, Latissimus Dorsi, and Teres Major. 



The Subanconeus is a small muscle, distinct from the Triceps, and analogous 

 to the Subcrureus in the lower limb. It may be exposed by removing the 

 Triceps from the lower part of the humerus. It consists of one or two slender 

 fasciculi, which arise from the humerus, immediately above the olecranon fossa, 

 and are inserted into the posterior ligament of the elbow-joint. 



Nerves. The Triceps and Subanconeus are supplied by the musculo-spiral 

 nerve. 



Actions. The Triceps is the great extensor muscle of the forearm ; serving, 

 when the forearm is flexed, to draw it into a right line with the arm. It is the 

 direct antagonist of the Biceps and Brachialis Anticus. When the arm is 

 extended, the long head of the muscle may assist the Teres Major and Latissi- 

 mus Dorsi in drawing the humerus backwards. The long head of the Triceps 

 protects the under part of the shoulder-joint, and prevents displacement of the 

 head of the humerus downwards and backwards. 



MUSCLES OF THE FOREARM. 



Dissection. To dissect the forearm, place the limb in the position indicated in Fig. 235 ; 

 make a vertical incision along the middle line from the elbow to the wrist, and a transverse 

 incision at each extremity of this ; the flaps of integument being removed, the fascia of the 

 forearm is exposed. 



The deep fascia of the forearm, continuous above with that inclosing the arm, 

 is a dense highly glistening aponeurotic investment, which forms a general 

 sheath inclosing the muscles in this region ; it is attached behind to the olecranon 

 and posterior border of the ulna, and gives off from its inner surface numerous 

 intermuscular septa, which inclose each muscle separately. It consists of cir- 

 cular and oblique fibres, connected together by numerous vertical fibres. It is 

 much thicker on the dorsal than on the palmar surface, and at the lower than 

 at the upper part of the forearm, and is strengthened by tendinous fibres, 

 derived from the Brachialis Anticus and Biceps in front, and from the Triceps 

 behind. Its inner surface gives origin to muscular fibres, especially at the 

 upper part of the inner and outer sides of the forearm, and forms the bounda- 

 ries of a series of conical-shaped cavities, in which the muscles are contained. 

 Besides the vertical septa separating each muscle, transverse septa are given 

 off both on the anterior and posterior surfaces of the forearm, separating the 



