THE POSTERIOR RADIOULNAR REGION 211 



ligament, fascia, and septa; there are three fleshy bellies, the 

 innermost divided into two, four passing under the posterior 

 annular ligament; the first and second pass to the index and 

 middle fingers connected by a weak band, always transverse; 

 the first is joined by the extensor indicis tendon at the meta- 

 carpophalangeal joint; the third runs to the ring finger and 

 sends a slip to the middle finger tendon; the fourth divides, 

 the outer larger part going to the ring finger, the inner part 

 joining the outer division of the extensor minimi digiti tendon; 

 this fourth is the smallest tendon, and receives muscular fibers 

 as far as the wrist. 



Opposite the metacarpophalangeal joints the tendons are 

 bound down by transverse fibers from the front of the joint, 

 ligamenta dorsalia; the tendon expands, is joined by a slip 

 from the interossei, and on the radial side by the insertion of 

 a lumbrical muscle, forming a broad aponeurosis, which divides 

 at the lower part of the first phalanx into three slips a central 

 thin one for the base of the second, while the two lateral parts 

 join and are inserted into the base of the last phalanx. 



2. M. extensor minimi digiti (extensor digiti quinti proprius) 

 rises from the superficial and deep fascia of the forearm, from 

 the orbicular ligament, from the septa between it and common 

 and ulnar extensors; its tendon is in a groove between the 

 radius and ulna, and splits into two on the back of the hand, 

 the outer being joined by a slip from the fourth common ex- 

 tensor tendon, and both parts end on the little finger, like 

 the other extensor tendons. 



3. M. Extensor Carpi Ulnaris (ulnaris externus). Origin, 

 common tendon, orbicular ligament, septa, fascia of the fore- 

 arm, which is connected with the elbow-joint capsule, and 

 anconeus; its belly in its middle third is bound to the posterior 

 border of the ulna by aponeurosis, and may receive fibers from 

 this fascia; insertion, tuberosity of the base of the fifth meta- 

 carpal. A bursa is under its tendon of origin in one-fourth 

 of the cases. 



In 52 per cent, of the cases a slip is continued anteriorly 

 over the opponens minimi digiti to the fascia over that muscle, 

 to the metacarpal bone or first phalanx of the little finger 

 (analogue of the peroneus brevis of the little toe). 



4. M. anconeus (quartus) fills the space between the triceps 

 and extensor carpi ulnaris; is flat and triangular, covered by 



