TRICEPS EXTENSOR AND ANCONEUS MUSCLES 207 



Tening between the tendon and the most prominent part of the ])rocess. 

 The middle or long head arises fi'om the lower part of the glenoid cavity 

 and an adjoining rough portion of the outer border of the scapula, by a 

 tendon which spreads over the sides of the muscular structure proceed- 

 ing from it. This head forms the middle and superficial part of the 

 common mass, presenting a long flat tendon on its posterior surfece 

 inferiorly. The external head takes origin by tendinous and fleshy 

 fibres along a line extending from the insertion of the teres minor, 

 downwards on the outer border of the humerus, as low as the musculo- 

 spiral groove, and fi'om an aponeurotic arch, formed by the external 

 intermuscular septum, as it crosses the upper part of the groove : its 

 fibres, which arc comparatively short, descend obliquely to be inserted 

 into the tendon of the middle part. The internal or deep head, the 

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

 humerus, beginning on the external aspect below the musculo-spiral 

 groove, and on the inner aspect of the arm reaching by a pointed process 

 as high as the insertion of the teres major : it also rises fi'om the 

 internal intermuscular septum in all its length, and fi'om 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. No muscular fibres arise from 

 the musculo-spiral groove itself. 



Itelations. — The long head of the triceps lies between the two teres muscles 

 above, and is in contact with the capsule of the shoulder-joint. The musculo- 

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

 and in the musculo-spiral gi-oove, pass between the inner and outer heads. 



Varhtk's. — The most frequent varieties of the triceps muscles 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, corresponding with the dorsi-cpitrockk'nrk or acccssoriiis 

 tric'qtltl which is common among quadi'umana. and exists in many other mam- 

 mals. The ('j)iti'ochlco-anconeus of Wenzel Gruber is a small muscle observed by 

 that author. Wood, and others, rising from behind the inner condyle, and inserted 

 into the olecranon. 



Subanconeus. — On removing the triceps from the lovi-er pai-t of the humerus, 

 some muscular fibres will be found passing from that part of the bone to the 

 capsule of the elbow-joint. These fibres, which ai'e analogous to the subcrureus 

 in the lower limb, have been described as distinct from the triceps under the 

 name subanconeus. 



The anconeus muscle, although placed chiefly below the elbow and 

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

 appropriately associated in description with that muscle. It arises by 

 a narrow tendon fi'om the extremity of the outer condylar eminence of 

 the humerus, at the posterior aspect. From this the fibres diverge 

 from one another, the upper being transverse, the rest passing down- 

 wards with increasing degrees of obliquity, and are inserted into the 

 olecranon on its radial aspect, and into the adjacent impression on the 

 upper third of the shaft of the ulna. Its superior fibres are parallel to 

 the lowest fibres of the internal head of the triceps, and are generally 

 in contact with them. 



Helafwn,^. — ^This muscle is subcutaneous in its whole extent. Its deep sm-facc 

 is in contact with the synovial membrane and external ligaments of the elbow- 

 joint. 



Vai-icties. — The anconeus varies chiefly in being more or less united to the 

 triceps or the extensor carpi ulnaris. 



