220 MYOLOGY. 



CAPUT MAGNUM. 



(Scapulo-olecraniics Magnus. ) 



(Fig. 78. d.) 



This, the great extensor of the fore-arm, is situated on the 

 posterior aspect of the shoulder. It is thick and triangular, 

 extending obliquely downwards and backwards, and consists of 

 several bundles, with tendinous intersections. 



Origin. — From the dorsal angle and posterior costa of the 

 scapula. 



Insertion. — By a strong tendon to the inner and upper part 

 of the olecranon, a synovial bursa being interposed between it 

 and the apex. It receives many fibres from the caput medium. 



Relation. — Externally with the fascia, the panniculus carnosus, 

 and the teres extern us, which occupies a depression in it ; inter- 

 nally with the latissimus dorsi, scapulo-ulnaris, and teres internus ; 

 inferiorly with the caput medium and caput parvum. 



Action. — To flex the shoulder joint, and extend the fore-arm. 



CAPUT MEDIUM. 

 {Humero-olecranius Externus.) 



(Fig. 78. c.) 



Placed between the preceding muscle and the humerus, it is 

 thick, short, and fleshy, extending obliquely backwards and down- 

 wards. 



Origin. — Aponeurotic, from a ridge on the supero-posterior 

 part of the shaft of the humerus, running from the deltoid ridge 

 to the neck. 



Insertion. — The supero-posterior part of the olecranon ; or it 

 may join the tendon of the caput magnum. 



Relation. — Superiorly with the caput magnum ; externally 

 with the teres externus ; inferiorly with the humeralis obliquus 

 and extensor metacarpi magnus ; internally with the caput parvum. 



Action. — To extend the fore-arm. 



