242 POSTERIOR BRACHIAL REGION. 



supinator brevis, tendon of the pronator radii teres, radius and wrist- 

 joint. By its ulnar border with the extensor communis digitorum. 



The EXTENSOR COMMUNIS DIGITORUM arises from the external 

 condyle, and intermuscular fascia ; and divides into four tendons, 

 which are inserted into the second and third phalanges of the fingers. 

 At the raetacarpo-phalangeal articulation each tendon becomes narrow 

 and thick, and sends a thin fasciculus upon each side of the joint. It 

 then spreads out and receiving the tendon of the lumbricalis, and some 

 tendinous fasciculi from the .interossei, forms a broad aponeurosis, 

 which covers the whole of the posterior aspect of the finger. At the 

 first phalangeal joint the aponeurosis divides into three slips. The 

 middle slip is inserted into the base of the second phalanx, and the 

 two lateral portions are continued onwards on each side of the joint, 

 to be inserted into the last. Little oblique tendinous slips connect the 

 tendons of the middle, ring, and little finger as they cross the back of 

 the hand. 



Relations. By its superficial surface with the fascia of the fore-arm 

 and back of the hand, and with the posterior annular ligament. By 

 its deep surface with the supinator brevis, extensor ossis metacarpi 

 pollicis, extensor primi internodii, extensor secundi internodii, extensor 

 indicis, posterior interosseous artery and nerve, wrist-joint, metacarpal 

 bones and interossei muscles, and phalanges. By its radial border 

 with the extensor carpi radialis longior and brevior. By the ulnar 

 border with the extensor minimi digiti, and extensor carpi ulnaris. 



The EXTENSOR MINIMI DIGITI (auricularis) is an off-set from the 

 extensor communis, with which it is connected by means of a tendi- 

 nous slip. Passing down to the inferior extremity of the ulna it tra- 

 verses a distinct fibrous sheath, and at the metacarpo-phalangeal articu- 

 lation unites with the tendon derived from the common extensor. The 

 common tendon then spreads out into a broad expansion which divides 

 into three slips to be inserted as in the other fingers into the last two 

 phalanges. It is to this muscle that the little finger owes its power 

 of separate extension ; and from being called into action when the 

 point of the finger is introduced into the meatus of the ear, for the 

 purpose of removing unpleasant sensations or producing titillation, the 

 muscle was called by the old writers " auricularis." 



The EXTENSOR CARPI ULNARIS arises from the external condyle 

 and from the upper two-thirds of the border of the ulnar. Its tendon 

 passes through the posterior groove in the lower extremity of the ulna, 

 to be inserted into the base of the metacarpal bone of the little finger. 



Relations. By its superficial surface with the fascia of the fore-arm, 

 and posterior annular ligament. By its deep surface with the supi- 

 nator brevis, extensor ossis metacarpi pollicis, extensor secundi inter- 

 nodii, extensor indicis, ulna, and wrist-joint. By its radial border it 

 is in relation with the extensor communis digitorum, and extensor 

 minimi digiti, and by the ulnar border with the anconeus. 



The ANCONEUS is a small triangular muscle having the appearance 

 of being a continuation of the triceps ; it arises from the outer condyle, 



