THE HAXD 



489 



.ONO. FLE 



middle and terminal phalanges being extended by the Interossei and Lumbri- 

 cales. It has also a tendency to separate the fingers as it extends them. The 

 Extensor minimi digiti extends similarly the little finger, and by its continued 

 action it assists in extending the wrist. It is owing to this muscle that the little 

 finger can be extended or pointed whilst the others are flexed. The chief action of 

 the Extensor ossis metacarpi pollicis is to carry the thumb outward and backward 

 from the palm of the hand, and hence it has been called the abductor longus 

 poUicis. By its continued action it helps to extend and abduct the wrist. The 

 Extensor brevis pollicis extends the proximal phalanx of the thumb. By its 

 continued action it helps to extend and abduct the wrist. The Extensor longus 

 pollicis extends the terminal phalanx of the thumb. By its continued action it 

 helps to extend and abduct the wrist. The Extensor mdicis extends the first 

 phalanx of the index finger, and by its continued action assists in extending the 

 wrist. It is owing to this muscle that the index finger can be extended or pointed 

 while the others are flexed. 



Surgical Anatomy. The tendons of the Extensor muscles of the thumb are liable to 

 become strained and their sheaths inflamed after excessive exercise, producing a sausage-shaped 

 swelling along the course of the tendon, and giving a peculiar creaking sensation to the finger 

 when the muscle acts. In consequence of its often being caused by such movements as wringing 

 clothes, it is known as ''washerwoman's sprain." 



THE HAND. 



Dissection (Fig. 301). Make a transverse incision across the front of the wrist, and a 

 second across the he&ds of the metacarpal bones : connect the two by a vertical incision in the 

 middle line, and continue it through the cen- 

 tre of the middle finger. The anterior and 

 posterior annular ligaments and the palmar 

 fascia should then be dissected. 



The Anterior Annular Ligament is 

 a strong, fibrous band which arches 

 over the carpus, converting the deep 

 groove on the front of the carpal 

 bones into a canal, beneath which 

 the flexor tendons of the 

 fingers. It is attached, internally, to 

 the pisiform bone and unciform pro- 

 f the unciform bone, and ex- 

 ternally to the tuberosity of the 

 scaphoid and to the inner part of the 

 anterior surface and the ridge on the 

 trapezium. It is continuous, above, 

 with the deep fascia of the forearm, of which it may be regarded as a thickened 

 portion, and. below, with the palmar fascia. It is crossed by the ulnar vessels 

 and nerve and the cutaneous branches of the median and ulnar nerves. At its 

 outer extremity is the tendon of the Flexor carpi radialis, which lies in the groove 

 on the trapezium between the attachments of the annular ligament to the bone. 

 It has inserted into its anterior surface the tendon of the Palmaris longus and 

 part of the tendon of the Flexor carpi ulnaris, and has arising from it, below, the 

 small muscles of the thumb and little finger. Beneath it pass the tendons of the 

 Flexor sublimis and profundus digitorum, the Flexor longus pollicis, and the 

 median nerve. 



The Synovial Membranes of the Flexor Tendons at the Wrist. There are two 

 synovial membranes which enclose all the tendons as they pass beneath this lig- 

 ament one for the Flexor sublimis and profundus digitorum, the other for the 

 Flexor longus pollicis. They extend up into the forearm for about an inch above 

 the annular ligament, and downward about halfway along the metacarpal bone, 

 where they terminate in a blind diverticulum around each pair of tendons, with 

 the exception of the thumb and sometimes the little finger in these two fingers 



FIG. 311. Transverse section through the wrist, show- 

 ing the annular ligaments and the canals for the passage 

 of the tendons. 



