THE ANTIBRACHIAL MUSCLES. 



60 1 



with the tendon of the extensor communis digitorum which passes to the little 



Brachialis anticus 



finger. 



Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral 

 nerve from the sixth, seventh, and 

 eighth nerves. Fig. 581. 



Action. — To extend the lit- 

 tle finger. 



Variations. — This muscle is some- 

 times absent, probably remaining in- 

 corporated in the extensor communis. 

 Its tendon occasionally sends a slip to 

 the fourth finger. 



6. Extensor Carpi Ulnaris 



(Figs. 577, 579). 



Attachments. — The exten- 

 sor carpi ulnaris arises in common 

 with the adjacent superficial ex- 

 tensors from the external condyle 

 of the humerus, from the deep 

 fascia, and, usually, from the apo- 

 neurosis attached to the posterior 

 border of the ulna common to 

 this muscle, the flexor profundus 

 digitorum, and the flexor carpi ul- 

 naris. Its tendon passes through 

 the sixth compartment beneath 

 the posterior annular ligament and 

 is inserted into the base of the 

 fifth metacarpal bone. 



Nerve-Supply. — By the 

 posterior interosseous branch of 

 the musculo-spiral nerve from the 

 sixth, seventh, and eighth cervical 



nerves. "^V \ ^ \ X" » A Radius 



Action. — To extend and ad- 

 duct the hand. 



Variations. — A fibrous band is 

 often given off from the tendon of the 

 muscle to be inserted somewhere over 



the fifth metacarpal into the sheath of the tendon of the extensor of the little finger ; it has 

 been termed the w. ulnaris quinti digiti. 



Olecranon, 



process 



External 



condyle 



Head of radius 



Anconeus. 



.Supinator 



Dissection of arm, showing deep muscles in vicinity of elbow. 



1. Supinator. 



2. Extensor ossis metacarpi pollicis. 



5 



{bb) The Deep Layer. 



3. Extensor brevis pollicis. 



4. Extensor longus pollicis. 

 Extensor indicis. 



I. Supinator (Figs. 580, 581). 



' Attachments. — The supinator, also termed the supinator radii brevis, is a flat 

 triangular muscle which arises partly from the outer condyle of the humerus and the 

 orbicular ligament of the elbow-joint, and partly from the upper part of the lateral 

 border of the ulna and the smooth surface beneath the lesser sigmoid cavity of that 

 bone. Its fibres pass obliquely downward and outward, diverging as they go, and 

 are inserted into the posterior, lateral, and anterior surfaces of the radius, curving 

 around that bone. The insertion extends downward to about the middle of the 

 radius. 



