POSTERO-EXTERNAL SCAPULAR REGION. 399 
ScaAPULO HUMERALIS POSTICUS is situated upon the posterior part of the 
shoulder. Origin—bifid; one part from the superior two-thirds of the 
inner surface of the posterior border of the scapula, the other from 
above the postero-internal surface of the glenoid cavity. Insertion—to 
the supero-posterior part of the humerus. <Actvion—it serves as a ligament, 
protecting the joint. 
TRICEPS EXTENSOR BRACHII (CAPUT PARVUM) is situated on the infero- 
internal part of the shoulder. Orvigin—from the internal and middle third 
of the humerus. Jnsertion—to the olecranon and to a tubercle on the 
supero-internal part of the ulna, close to the olecranon. Action—to 
extend the arm. 
POSTERO-EXTERNAL SCAPULAR REGION. 
TRICEPS EXTENSOR BRACHII (CAPUT MAGNUM) is situated upon the infero- 
posterior part of the shoulder, occupying the angular interspace between 
the scapula and humerus. Ovzgin—from the whole length of the posterior 
border as high up as the supero-posterior angle of the scapula. Jnsertion— 
to the inner and upper part of the olecranon. Actvon—to approximate the 
scapula and humerus, and thus raise the elbow joint ; if the former is fixed, 
to extend the arm. 
TRICEPS EXTENSOR BRACHII (CAPUT MEDIUM) lies upon the infero-external 
part of the shoulder and humerus. Origin—from the humerus, just behind 
a ridge at the postero-external part of the superior third. J/nsertcon— 
to the supero-external and posterior part of the olecranon, Action—to 
extend the arm. 
TERES EXTERNUS is situated upon the postero-external part of the 
shoulder. Origin—irom a little tubercle just below the supero-posterior 
angle, and from the lower border of the scapula. Jnsertion—to a ridge 
descending from the outer tubercle of the humerus, and to the hgament 
which extends from the outer tubercle to the outer condyle of the same 
bone. Action—to flex the scapula on the humerus, or the humerus on 
the scapula. 
ScAPULO HUMERALIS EXTERNUS lies upon the postero-external part of the 
shoulder. Ovigin—from the inferior two-thirds of the posterior border 
of the scapula, just above the glenoid cavity, and from its dorsal surface, 
Insertion—to the middle of the ridge extending from the outer tubercle 
of the humerus. * Actton—to flex the humerus, and draw it outwards, 
THE ANTERO-EXTERNAL HUMERAL REGION. 
HUMERALIS EXTERNUS lies on the infero-external side of the upper 
arm. Origin—from the infero-posterior, inner, and outer surface of the 
body of the humerus, and winds round that bone. Jnsertton—to the 
supero-anterior and internal part of the radius. Action—to flex the arm. 
THE POSTERO-INTERNAL HUMERAL REGION. 
ANnconzvs is situated upon the hollow space between the condyles, 
Origin—from the supero-posterior part of the lower third of the humerus. 
Insertion—to the antero-external border of the ulna and capsular ligament 
of the joint. Action—to extend the elbow, and to protect the capsular 
ligament during the movement between the two bones 
