Subscapularis (Unterschulterblattmuskel). Springs from the inner surface of the scapula, except from the suprascapula, goes with converging fibers directly over the capsule of the shoulder joint to be attached to the medial process of the humerus.
Anconæus. This strong muscle lies on the extensor side of the upper arm. It is made up of two layers: the superficial comes from the pectoral girdle in two heads: (a) the caput scapulare laterale externum and (b) caput coraco-scapulare; the deeper layer originates on the humerus by three heads, (c) caput humerale laterale, (d) caput humerale posticum, and (e) caput humerale mediale. These five heads of the anconæus muscle with their synonyms will now be described.
(a) Caput Scapulare Laterale Externum ([Plate I.], Figs. 1 and 4, asl) (Brevi proximum caput m. tricipitis, Gewöhnlicher [äusserer] langer Kopf des dreiköpfigen Streckers, Portion scapulaire externe du triceps-brachial, Erster langer Kopf des Triceps, [Zweiter] abducirender vom Schultergerüst entstehender Kopf des Streckmuskels des Vorderarmes, Triceps Nr. 1, Triceps longus). This muscle springs as a tendon from the hinder border of the scapula directly beneath the articular cavity, and extends back, between the scapulo-humeralis profundus and the dorsalis scapulæ muscles, into the muscle belly.
(b) Caput coraco-scapulare ([Plate I.], Figs. 2, 4, 5, 6, acs) (Externum caput m. tricipitis, Innerer langer Kopf des dreiköpfigen Streckers, Portion scapulaire interne du triceps-brachial, Zweiter langer Kopf des Triceps, [Erster] abducirender vom Schultergerüst entstehender Kopf des Streckmuskels des Vorderarmes, Triceps Nr. 2, Triceps longus secundus). Arises by two distinct tendinous tips—the upper, weaker one from the hinder border of the scapula, the lower, broader one from the hinder border of the coracoid.
(c) Caput Humeri Laterale ([Plate I.], Figs. 1 and 4, ahl) (Brevius caput m. brachiei interni, [Aeusserer] kurzer Kopf des dreiköpfigen Streckers, Portion huméral externe du triceps brachial, Aeusserer vom Humerus ausgehender Kopf des Streckmuskels des Vorderarmes, Theil des Triceps Nr. 3, Triceps externum). Springs from the lateral part of the extensor surface of the humerus dorsal to the lateral process and the origins of the humero-radialis and brachialis superior.
(d) Caput Humerale Posticum ([Plate I.], Fig. 4, ahp) (Longissimum caput m. brachiei internum, Theil des inneren [kurzen] Kopfes des dreiköpfigen Streckers, Theil des Triceps Nr. 3, Theil des Triceps internus, Theil der Portion humérale interne du triceps brachial, [Mittler] vom Humerus ausgehender Kopf des Streckmuskels des Vorderarmes). Springs from the middle of the extensor surface of the humerus between the lateral and medial heads.
(e) Caput Humerale Mediale (Longius caput m. brachiei interni, Theil des [inneren] kurzen Kopfes des dreiköpfigen Streckers, Theil der Portion humérale interne du triceps brachial, [Innerer] vom Humerus ausgehender Kopf des Streckmuskels des Vorderarmes, Theil des Triceps Nr. 3, Theil des Triceps internus). This head originates on the medial part of the extensor surface of the upper arm at the end of the medial process where it is united with the scapulo-humeralis profundus muscle.
The muscle mass formed by the union of all the above heads goes over, as a broad and somewhat thick tendon, to become inserted on the proximal part of the ulna.
Humero-radialis ([Plate I.], Figs. 1 and 4, hr) (Caput longum m. bicipitis, Eigener kurzer Beuger, [Zweiter] vom Oberarm ausgehender Beuger, Brachialis externus, Portion a of Brachiæus). A fairly large muscle on the outer side of the upper arm, lying between the brachialis inferior and caput humerale laterale muscles, with both of which it is, at the beginning, united. It originates with its deeper and chief mass from the outer surface of the humerus, just distal to the lateral process; while its superficial layer, especially the upper fibers, come directly from the deltoides scapularis inferior and therefore have their origin on the scapula. In the middle of the upper arm it becomes a slender round tendon that extends, through a tendinous loop, to the radius, on whose outer side, at the end of the proximal third, it is inserted.