TRICEPS EXTENSOR AND ANCONEUS MUSCLES. 221 



ligament of the elbow-joint, and terminates below in a thick mass which is inserted 

 into the inner part of the rough triangular surface on the front of the coronoid 

 process and the tuberosity of the ulna. 



Relations. This muscle lies immediately behind and projects on each side of the biceps. 

 It supports the brachial vessels and median nerve. On the outer side the musculo- spiral 

 nerve lies upon it, under cover of the supinator longns. 



Varieties. The most frequent varieties of this muscle consist in its subdivision into two 

 or sometimes more parts ; its union with neighbouring- muscles, such as supinator longus, 

 pronator teres or biceps ; insertion of a slip from it into the semilunar fascia ; and occasion- 

 ally into the radius. 



The triceps extensor cubiti (figs. 232, 233) occupies the whole posterior 

 brachial region. The muscle consists of three separate portions or heads, which are 

 united below in a common tendon occupying the posterior surface of the mass from 

 the middle of the arm to the elbow, where it terminates by being inserted into the 

 olecranon process of the ulna. The middle or long head arises from the rough 

 triangular impression on the lower part of the neck, and the adjacent portion of the 

 axillary border of the scapula, by a tendon which spreads over the surface of the 

 muscular structure proceeding from it. This head forms the middle and superficial 

 part of the muscle, and its fibres end on the inner margin of the common tendon. 

 The external head takes origin by tendinous and fleshy fibres from the upper and 

 outer part of the posterior surface of the humerus, extending from the insertion of 

 the teres minor downwards as low as the groove of the musculo-spiral nerve, and 

 from an aponeurotic arch formed by the external intermuscular septum as it crosses 

 this groove : its fibres, which are comparatively short, descend obliquely to be 

 inserted into the upper end and outer border of the tendon. The internal or deep 

 head, the shortest of the three, arises from the whole extent of the posterior surface 

 of the humerus below the spiral groove, on the inner aspect of the arm reaching by 

 a pointed process as high as the insertion of the teres major ; it also arises from the 

 internal intermuscular septum in all its length, and from the inferior portion of the 

 external septum. Some of its lower fibres are inserted immediately into the 

 olecranon, but the greater part of them join the deep surface of the common tendon. 

 The insertion of the common tendon takes place mainly into the tuberosity of the 

 oleeranon ; but from its outer side a considerable band is prolonged downwards over 

 the anconeus, blending with the fascia of the forearm, in which the fibres can be 

 followed to the posterior border of the ulna. 



Relations. The long head of the triceps lies between the two teres muscles above, and is 

 closely connected to the capsule of the shoulder- joint. The musculo-spiral nerve and the 

 superior profunda artery are deeply imbedded in the muscle, and in the spiral groove pass 

 between the inner and outer heads. 



In many cases there is a small bursa above the olecranon, either between the tendon of 

 the triceps and the posterior ligament, or more frequently in the deep part of the tendon 

 itself. A bursa behind the internal condyle, beneath the inner edge of the triceps and the 

 ulnar nerve, is of rare occurrence. (Gruber, >; Die Bursae mucosa3 cubitales," 1866.) 



Varieties. The most frequent varieties of the triceps muscle are the following, viz. : 1, 

 an additional or fourth head arising from the inner part of the humerus, above or near the 

 inner head ; and 2, a slip of connection between the triceps and the latissimus dorsi, corre- 

 sponding with the doi'so-ejtitrocltlearis or acvessurius triciitit-i.t which is common among 

 quadrumana, and exists in many other mammals. 



Subanconcus. On removing the triceps from the lower part of the humerus. a few 

 muscular fibres are sometimes found passing from that part of the bone to the capsule of the 

 elbow -joint. These fibres, which are analogous to the subcrureus in the lower limb, have been 

 described as distinct from the triceps under the name subanconeu*. 



The anconeus muscle (fig. 232, 9), although placed chiefly below the elbow and 

 in the forearm, is intimately connected with the triceps, and may be appropriately 

 associated in description with that muscle. It arises by a narrow tendon from an 



