MUSCLES OF THE OUTSIDE OF THE SHOULDER. '235 



and extends the arm or humerus upon the scapula, and moves 



it forward 



See the description at b. 



k. The postea spinatus muscle, situated behind the spine or ridge, 

 and occupying the space called the fossa postea spinata. It 

 extends to the lower bone of the shoulder, and is inserted into 

 the upper head of that bone. It is of a triangular form, and is 

 flattened, and broader, but not so thick in substance as the 

 antea spinatus muscle. It assists the flection of the hume- 

 rus, and at the same time rolls it outwards. This is the 

 tendon of the long extensor of the arm, which reaches from 

 the upper angle and the posterior border of the scapula, to the 

 point of the elbow and the inside of the arm. This muscle is 

 a very important one. 

 f», g, t, Are the three divisions of another muscle concerned in the 

 same oflBce with p, arising from the shoulder-blade and the 

 lower bone of the shoulder, and likewise attached to the point 

 of the elbow by a veiy powerful tendon. 

 t This is the middle flexor, which is one of the numerous and 

 powerful muscles which bend the leg. It is also represented 

 at e, plate vi. fig. 2, and is the muscle which bends the shank- 

 bone, because it is situated precisely in the middle of the back 

 part of the arm. It has its origin from the inner head of the 

 lower bone of the shoulder, and is inserted into one of the 

 bones on the inner side of the knee. The other is seen at 2, 

 fig. 1, and is called the external flexor of the leg, in conse- 

 quence of lying on the outer side of the arm, towards the 

 back. It is inserted on the outer head of the lower bone of 

 the shoulder ; advancing towards the knee, it is tendinous ; and 

 the tendon divides into two portions, one of which is inserted 

 into the same bone of the knee, and the other into the outer 

 small bone of the leg. The internal flexor is exhibited at g, 

 plate vi. fig. 2. 



n. This is one of the muscles of the lower bone of the shoulder. 

 It is the external one, whose oflSce is to bend the arm. It 

 arises fi-om the inner and back part of the neck and body oi* 

 the lower bone of the shoulder, and turns obliquely round it, 

 and is inserted into the inner and upper part of the bone of 

 the arm. 



