86 Anatomy of Skeleton 



fibrous and serous coverings : it gives its bicipital or articular branch upwards in the groove, and 

 some small foramina in the upper part of the groove receive minute twigs from this. 



The artery itself proceeds transversely, crossing the outer lip above the pectoral tendon, and 

 therefore piercing the upper expansion of the tendon : it now finds itself on the surface of the bone 

 covered by the Deltoid. 



Deltoid. The insertion is by strong tendon on the outer and front aspect of the 

 shaft, but the posterior fibres tend to turn under the more external ones, and to reach 

 the back and outer side of the bone at a slightly higher level : the roughness they 

 cause on the bone may extend some distance up the back of the shaft. The front 

 part of the muscle altogether covers the tendon of insertion of Pectoralis major 

 (Fig. 65). 



Triceps.- Outer head : attached below to back of Deltoid tendon, and extending 

 up to get just under cover of the lower border of Teres minor, a little distance 

 internal to its insertion. If a thick line is drawn from this point to the back of the 

 deltoid impression it will mark the attachment, for the origin is by compressed 

 tendon. 



Inner head : extends upwards internally, passing under cover of Teres major for 

 some | | inch (Fig. 67). Sometimes these fibres are aponeurotic, making a mark on 

 the bone just behind the Teres ridge, but they are frequently muscular and cause no 

 roughness : the position of the muscle, however, is constant here. The area of origin 

 is as shown in Fig. 63, and extends down farther on the outer than on the inner side. 

 When the head is in position it is evident that the musculo -spiral nerve and superior 

 profunda artery must lie on it and cross it to reach the groove, which is really outside 

 this head of the muscle : this is the only part where these structures run in contact 

 with the bone (see Fig. 67). 



There are only two planes in the Triceps. The inner head, lying on and arising from the bone, 

 is deep to the other two heads, which lie side by side behind it. Thus the musculo-spiral nerve, 

 sinking back below the Teres major, disappears from view on the inner side of the arm by passing 

 between the long and inner heads : it crosses the latter head, covered by the former, and then 

 passes under cover of the outer head and reaches the bone outside the inner head. The circumflex 

 nerve, passing back above the Teres major, goes between outer and long heads, and its anterior 

 division crosses the former under cover of Deltoid while the posterior division crosses the long head, 

 under the Deltoid to reach its lower border and turn round it. The ulnar nerve runs in a straight 

 line from the Teres major along the inner side of the inner head just behind the internal inter- 

 muscular septum, and the septum reaches the prominent internal condyle, so the nerve passes 

 behind the condyle, coming into contact with the bone here and passing on to the internal lateral 

 ligament below. 



External Intermuscular Septum is attached to the outer supracondylar ridge. If 

 the ridge is traced up, it is found to lead toward the back of the deltoid impression, 

 but is lost before reaching it owing to the depression of the spiral groove. The septum 

 may be looked on as derived from the back of the Deltoid tendon, or, perhaps more 

 truly, as a continuation down of the line of origin of the outer head of Triceps from the 

 point where it is attached to the back of the tendon. Brachialis anticus arises from 

 the bone in the angle between the line of the septum and the Deltoid tendon, but is 

 separated from the septum below this by the origin of Supinator longus (upper two 

 thirds) and Extensor carpi radialis longior (lower one-third) from the front of the 

 external ridge in front of the septum. The last-named muscle has a prominent marking 

 on the bone. 



Brachialis anticus shows individual variation to some degree in the distance to 

 which its origin extends behind the Deltoid : also in its upward extension between 



