DISSECTION OF THE ANTERIOR LIMB. 19 



These two tendons are in contact with the capsular ligament of the 

 joint, and the tendon of origin of the biceps emerges from between them. 

 Action. — It is an extensor of the shoulder-joint. 



Directions. — The outer aspect of the triceps extensor cubiti is here 

 seen ; and, when its -surface has been cleaned, a line will be observed 

 running from the shoulder to the point of the elbow. Careful dissec- 

 tion downwards into the mass, along this line, will separate the caput 

 magnnm (already described) from the caput medium, which lies below 

 it. While the surface of the muscle is being cleaned some small 

 cutaneous nerves from the musculo-spiral will be found to pierce the 

 muscle, or emerge at its lower edge, and become distributed to the outer 

 side of the fore-arm. These should, as far as possible, be preserved. 



The Caput Medium (Plates 7 and 8) arises, by a short aponeurotic 

 tendon, from a curved line beginning ou the deltoid tubercle and 

 continued upwards to the external tuberosity. It is inserted into the 

 olecranon. 



Action. — Like the other divisions of the triceps, this muscle is an 

 extensor of the elbow-joint. 



Directions. — By raising the lower edge of the last muscle and dis- 

 secting upwards, the anconeus will be partly exposed ; but to effect a 

 complete and natural separation of the two muscles is a matter of 

 some difficulty. 



The Anconeus (Plates 7 and 8) is a small muscle which lies above 



the olecranon fossa, and there covers the synovial membrane of the 



joint, a pad of fat being interposed. It arises from the margin of the 



fossa, and is inserted into the olecranon on its outer and anterior aspect. 



Action. — To assist in extending the elbow. 



Directions. If the caput medium be now severed at its origin, and 



turned backwards, the musculo-spiral nerve and some branches of the 

 deep humeral artery will, as already described, be found turning round 

 the humerus in the musculo-spiral groove, which is mainly filled by the 

 brachialis anticus muscle. 



The Brachialis Anticus muscle (Plate 8), also known as the 

 humeralis obliquus or externus, is lodged in the furrow of torsion on 

 the shaft of the humerus. The muscle has its origin on the posterior 

 aspect of the shaft of the humerus below its articular head. Its tendon, 

 which cannot be followed at present, passes in front of the elbow-joint, 

 and is afterwards reflected under the internal lateral ligament of the 

 joint, to be inserted into the radius and ulna. 

 Action.— To flex the elbow-joint. 



THE FORE-ARM. 



Surface-marking.— k.t the elbow-joint the olecranon process of the 

 ulna is distinctly seen; but the shafts of the bones of the fore-arm are 



