274 



The Muscles of Fore-arm 



The pronator quadratus arises from the front of the lowest fourth 

 of the ulna and is inserted into the corresponding surface of the radius. 

 Its nerve is the anterior interosseous. 



Relations. It is covered by the tendons ot the flexors profundus 

 digitorum, longus pollicis, and carpi radialis, and by the radial artery 

 and its venae comites. The ulnar artery is widely separated from it 

 by the mass of the flexor profundus tendon and muscle. 



Of the synovial membranes beneath the anterior annular liga- 

 ment, one surrounds the tendons of the flexors sublimis and profundus 

 together with the median nerve as they pass beneath the ligament. As 

 the tendons lie in the fibrous sheaths on the front 

 of the first and second phalanges they are also 

 invested by synovial bursae, but these bursae are 

 distinct from the membrane beneath the annular 

 ligament. In the case of the little finger, however, 

 the synovial membrane from beneath the annular 

 ligament is directly continuous with that which 

 lines the digital sheath, as is shown in the adjoin- 

 ing wood-cut. The synovial sheath does not de- 

 scend on to the ungual phalanx, for at the base of 

 that bone the tendon of the deep flexor is inserted. 

 The outer synovial membrane beneath the annular 

 ligament accompanies the tendon of the flexor 

 longus pollicis down into the fibrous sheath along 

 the metacarpal bone and the first phalanx of the 

 thumb. The two large synovial bursae beneath the annular ligament 

 are separated from one another by the median nerve ; they extend into 

 the fore-arm about an inch above the annular ligament. 



A reference to the wood-cut shows that a deep inflammation ot 

 the thumb or of the little finger is likely to lead to more serious 

 complications than that of the second, third, or fourth fingers, as, the 

 digital pouch of synovial membrane being implicated, suppuration may 

 extend beneath the annular ligament and up into the fore-arm. Some- 

 times the inner and outer pouches communicate above the wrist by a 

 tubular process across the median nerve, in which case a deep-seated 

 suppuration in the thumb may eventually implicate the sheath of the 

 flexor tendons of the little finger, the sheaths in the intermediate digits 

 being unaffected. 



In the case of acute suppuration in one or other of these burs;i- it is 

 expedient to lay it freely open, dividing the annular ligament at the 

 same time. The purulent swelling bulges in the fore-arm and in the 

 hand, and, being constricted beneath the ligament, is somewhat of 

 hour-glass shape. When the sheath of one of the three middle digits 

 only is affected, it is better to incise the thecal abscess over the head 

 of the metacarpal bone than to slit open the sheath down the first and 

 second phalanges, with the risk of producing a stiff and comparatively 

 useless finger. 



Usual arrangement 

 synovial sheaths 

 palm. 





