FLEXOR AND PROXATOR MUSCLES. 215 



fibres are inserted immediately into the olecranon, and the greater part of 

 them join the deep surface of the common tendon. No muscular fibres 

 arise from the musculo-spiral groove itself. 



The method of description above followed, in which all the fibres arising below the 

 musculo-spiral groove are assigned to the internal head, originated with Theile. 

 (Miiller's "Archiv," &c. 1839, p. 420, and "Soemmerring v. Baue," &c.) The long 

 head of the triceps lies between the two teres muscles above, and is in contact with the 

 capsule of the shoulder-joint. The musculo-spiral nerve, and the superior profunda 

 artery, pass between the inner and outer heads as they lie in the musculo-spiral 

 groove. 



Subanconeu$.0n removing the triceps from the lower part of the humerus, some 

 muscular fibres will be found passing from that part of the bone to the capsule of the 

 elbow-joint. These fibres, which are analogous to the subcrureus in the lower limb, 

 have been described as distinct from the triceps under the name subanconeus. 



The anwneus muscle (anconeus quartus) although placed below the elbow 

 and in that respect belonging to the forearm, is in its structure, function 

 and nervous supply, so intimately connected with the triceps, that it is most 

 appropriately associated in description with that muscle. It arises by a 

 narrow tendon from the extremity of the outer condyloid eminence of the 

 humerus, at the posterior aspect. From this the fibres diverge from one 

 another, the upper being horizontal, the rest passing downwards with in- 

 creasing degrees of obliquity, and are inserted into the olecranon on its 

 radial aspect, and into the adjacent impression on the upper third of the 

 shaft of the ulna. Its superior fibres are parallel to the lowest fibres of the 

 internal head of the triceps, and are generally in contact with them. 



ACTIONS. The biceps muscle raises the arm at the shoulder and flexes the elbow- 

 joint ; the long head of the triceps depresses the arm at the shoulder, and extends the 

 elbow-joint. The short head of the biceps draws the arm inwards as well as upwards, 

 as does also the coraco-brachialis. If the biceps be called into action when the hand 

 is in pronation, its first effect, in virtue of its insertion into the back part of the 

 tuberosity of the radius, is to produce supination of the forearm. The brachialis 

 anticus is a simple flexor of the elbow; the external and internal heads of the triceps, 

 and the anconeus muscle, are simple extensors of that joint. 



MUSCLES OF THE FOREARM. 



a. Anterior and Inner Regions (Flexors and Pronator s). 



The muscles on the front and inner part of the forearm are disposed 

 in two sets, one being superficial, the other more deeply seated. 



The superficial layer of muscles comprehends the pronator radii teres, 

 flexor carpi radialis, palmaris longus, flexor carpi ulnaris and flexor digito- 

 rum sublimis. These five muscles are intimately united at their origin from 

 the inner condyle, to which they are attached by a common tendon which 

 gives fibres to each, and also sends septa between them. 



The pronator radii teres, the most external of the group, arises by two 

 distinct heads; one, large and superficial, is derived from the upper part of 

 the inner condyloid eminence of the humerus, and from the common tendon 

 above mentioned ; also from the fascia and the intermuscular septum of the 

 forearm. The second head, a thin fasciculus deeply placed, conies from 

 the inner margin of the coronoid process, and joins the other at an 

 acute angle. The fleshy belly thus formed proceeds outwards and down- 



