220 MYOLOGY. 



CAPUT MAGNUM. 



(Scapnlo-olecraniuft Magnus. ) 



(Fio. 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 externus, 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. ) 

 (Fio. 78. e.) 



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. 



