_Origin_ (Fig. 83, _g_, _g′_) from a long V-shaped line two to four millimeters wide on the lateral surface of the humerus. The apex of the V is just distad of the teres minor tubercle (_d_). Its dorsal limb (_g′_) extends along the lateral supracondyloid ridge to a point opposite the proximal margin of the supracondyloid foramen; its ventral limb (_g_) extends in the direction of the deltoid ridge to the middle of the bone. No muscle-fibres take origin between the two limbs. The fibres converge and end in a flat tendon which joins the tendon of the clavobrachial (Fig. 79, _k_). _Insertion_ (Fig. 87, _c_).--The dorsal portion of the depressed rough area on the lateral surface of the ulna just distad of the semilunar notch. _Relations._--Outer surface with the acromiodeltoid (Fig. 75, _f_), the caput laterale of the triceps (Fig. 75, _h_), the brachioradialis (Fig. 75, _k_), and the proximal end of the extensor carpi radialis longus (Fig. 75, _l_). Inner surface with the humerus. Medial edge with the pectoralis major (Fig. 65, _l_) and the biceps (Fig. 77, _g_). _Action._--Flexor of the antibrachium. =M. triceps brachii.=--The triceps muscle of the cat, like that of man, is divisible (as its name indicates) into three main portions. These are a lateral portion (caput laterale), an intermediate or long portion (caput longum), and a medial portion (caput mediale). The first two correspond to the similarly named heads in man; the medial portion falls into a number of subdivisions whose homologues are uncertain. [Illustration: FIG. 79.--DEEP MUSCLES ON THE MEDIAL SIDE OF THE HUMERUS. _a_, M. supraspinatus; _b_, M. subscapularis; _c_, M. coracobrachialis; _d_, M. teres major (_d′_, its tendon); _e_, part of M. latissimus dorsi joining the teres major; _f_, cut end of M. pectoralis minor; _g_, long part of caput mediale of M. triceps brachii; _h_, intermediate part of caput mediale of M. triceps; _i_, M. brachialis (_i′_, its tendon); _j_, short part of caput mediale of M. triceps; _k_, cut end of M. clavobrachialis; _l_, _l′_, cut ends of M. biceps; _m_, M. brachioradialis; _n_, M. extensor carpi radialis longus; _o_, M. extensor carpi radialis brevis; _p_, fifth head of M. flexor profundus digitorum; _q_, first head of M. flexor profundus digitorum. 1, humerus; 2, olecranon; 3, medial epicondyle of humerus.] =Caput laterale= (anconeus lateralis) (Fig. 75, _h_; Fig. 68, _l_).--The lateral portion is a flat muscle (most of it subcutaneous) on the lateral side of the brachium, connecting the proximal end of the humerus with the olecranon process of the ulna. _Origin_ (Fig. 81, _h′_).--By a flat tendon from the proximal portion of the deltoid ridge and the distal border of the teres minor tubercle. _Insertion_ (Fig. 86, _c_) by a thin, flat tendon into the lateral border of the dorsal surface of the ulna between a point opposite the distal margin of the semilunar notch and the proximal end of the olecranon.