POSTERIOR HUMERAL REGION. 



209 



Fig. 83.* 



Considered in relation to their length, these heads have been named 

 long, short, and middle ; and in reference to their position, internal, 

 external, and middle ; the term middle, in the former case, referring 

 to the external head, and in the latter case to the long head. This 

 has given rise to much confusion and misunderstanding. I shall, 

 therefore, confine myself to the designations derived from their rela- 

 tions. The external head arises from the humerus immediately 

 below the t insertion of the teres minor. The internal head (short) 

 arises from the humerus immediately below the insertion of the teres 

 major. The scapular head (long) lies be- 

 tween the two others, and arises from the 

 upper third of the inferior border of the sca- 

 pula. The three heads unite to form a broad 

 muscle, which is inserted by an aponeurotic 

 tendon into the olecranon process of the 

 ulna ; a small bursa is situated between its 

 . tendon and the upper part of the olecranon. 



The scapular head of the triceps passes 

 between the teres minor and major, and di- 

 vides the triangular space between those two 

 muscles into two smaller spaces, one of 

 which is triangular, the other quadrangular. 

 The triangular space is bounded by the teres 

 minor, teres major, and scapular head of the 

 triceps ; it gives passage to the dorsalis sca- 

 pulae artery and veins. The quadrangular 

 space is bounded on three sides by the three 

 preceding muscles, and on the fourth by the 

 humerus. Through this space pass the pos- 

 terior circumflex artery and veins, and cir- 

 cumflex nerve. 



Relations. By its posterior surface with 

 the deep and superficial fascia and integu- 

 ment. By its anterior surface with the supe- 

 rior profunda artery, musculo-spiral nerve, 

 humerus, intermuscular aponeurosis which 



separates it from the brachialis anticus, and with the elbow-joint. 

 The scapular head is in relation posteriorly with the deltoid and 

 teres minor; anteriorly with the subscapularis, teres major, and 

 latissimus dorsi ; and externally with the posterior circumflex ves- 

 sels and nerve. 



Actions. The triceps is an extensor of the fore-arm. 



* A posterior view of the upper arm, showing the triceps muscle. 1. Its external 

 head. 2. Its long, or scapular head. 3. Its internal, or short head. 4. The olecranon 

 process of the ulna. 5. The radius. G. The capsular ligament of the shoulder-joint. 



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