MUSCLES OF THE ANTERIOR LIMBS, 259 



the olecranon, after receiving a great number of fibres from the short extensor, 

 and after gliding, by means of a synovial capsule, over the eminence which 

 serves for its insertion. 



Relations. The external surface is covered by a thin, fibrous, white-and- 

 yellow elastic layer, which separates it from the panniculus ; it is hollowed, 

 near the upper border of the muscle, by an excavation into which is received 

 the posterior portion of the long abductor. Its internal face responds to 

 the great dorsal, the adductor of the arm, and to the long extensor. Its posterior 

 border is margined by the latter muscle ; the superior follows the axillary 

 border of the scapula, and is attached to it to constitute the fixed insertion 

 of the muscle ; the inferior responds to the short and middle extensors. 



Action. It is an extensor of the fore-arm. 



3. Short Extensor of the Fore-arm. (Fig. 119, 8.) 



Synonyms. Humero-olecranius externus Girard. The vastus externus of the 

 triceps brachialis of Man. (Caput medium PercivaU.) 



Situation Direction Form Structure. This muscle is situated 

 between the humerus and the inferior border of the preceding, and is 

 directed obliquely downwards and backwards. It is thick and short, 

 flattened and aponeurotic at its upper extremity, prismatic, and entirely 

 formed of thick parallel muscular fasciculi for the remainder of its extent. 



Attachments. One of its attachments is on the humerus, to the curved 

 line extending from the deltoid imprint to the base of the articular head 

 (see for this line Fig. 41, above 4), by the short aponeurosis of its superior 

 extremity fixed insertion ; the other is to the olecranon, either directly, or 

 through the tendon of the large extensor movable insertion. 



Relations. The prismatic shape of this muscle offers three faces, which 

 respond : externally, to the two abductors of the arm and to a slight fibrous 

 layer continuous, above, with that which covers the large extensor, and below, 

 with the antibrachial aponeurosis ; internally, to the small extensor, from 

 which it is difficult to separate it, to the short flexor of the fore-arm, and to 

 the anterior extensor of the metacarpus ; superiorly, to the large extensor, 

 which closely adheres to it. 



Action. An extensor of the fore-arm. 



4. Middle Extensor of the Fore-arm. (Figs. 119, 17; 121, 8.) 



Synonyms. Humero-olecranius internus Girard. The vastus internus of the 

 triceps brachialis of Man. (Caput parvum Percivall.') 



Situation Direction Form Structure. This muscle is situated at 

 the internal face of the humerus, along the inferior border of the large 

 extensor. It is oblique downwards and backwards, pyriform, bulging at its 

 superior extremity, contracted inferiorly, where it terminates by two small 

 flat tendons. 



Attachments. It originates, by its superior extremity, from the inner 

 aspect of the humerus, behind and above the tuberosity on its body. One 

 of its terminal tendons is attached to the summit of the olecranon ; the 

 other glides over a small convexity on the inner side of that eminence, and 

 goes to be inserted a little lower than the first. 



Relations. Above, with the inferior border of the large extensor ; out- 

 wards, with the humerus, the short flexor, and short extensor of the fore- 

 arm ; inwards, with the humeral insertion of the great dorsal and the 

 adductor of the arm, the long branch of the coraco-brachialis, the vessels 



