THE UPPER LIMB i77 



and converts it into a fibro-osseous canal. Externally it is attached 

 to the tuberosities of the scaphoid and trapezium, and internally to 

 the pisiform and hook of the unciform. Its upper border is con- 

 tinuous with the deep fascia of the front of the forearm ; its lower 

 border is connected with the palmar fascia ; at its upper and inner 

 part it receives an expansion from the tendon of the flexor carpi 

 ulnaris ; and near its lower border it gives partial insertion to the 

 tendon of the palmaris longus. The ligament is crossed by the last- 

 mentioned tendon and the ulnar vessels and ner\'e, the latter 

 structures lying close to the pisiform bone, where they are overhung 

 by it, and overlapped by a slip from the flexor carpi ulnaris. At 

 either side the ligament affords origin to muscles of the thenar and 

 hypothenar groups. The fibro-osseous canal formed by the liga- 

 ment and front of the carpus gives passage to the tendons of the 

 flexor sublimis and flexor profundus digitonun, the tendon of the 

 flexor longus poUicis, and the median nerve. The tendon of the 

 flexor carpi radialis does not pass through this canal, but traverses 

 a special compartment in the outer part of the ligament as it passes 

 through the groove on the front of the trapezium, where it is invested 

 by a special synovial sheath. 



Thenar Muscles. — ^The short muscles of the thumb are five in 

 number, namely, the abductor, opponens, and flexor brevis, pol- 

 licis, the adductor obliquus pollicis, and the adductor transversus 

 polUcis. 



1. Abductor Pollicis — Origin. — (i) The front of the anterior 

 annular ligament ; (2) the tuberosity of the scaphoid ; and (3) the 

 tuberosity of the trapezium. 



Insertion. — (i) The outer side of the base of the first phalanx of 

 the thumb, in association with the superficial head of the flexor 

 brevis pollicis ; and (2) the outer margin of the tendon of the ex- 

 tensor longus poUicis on the back of the first phalanx. 



Nerve-supply. — ^The median nerve. 



The muscle, which is triangular, is directed downwards and out- 

 wards. 



Action. — (i) To abduct the thumb, and (2) to assist in flexing its 

 first phalanx, the result being that the thumb is drawn forwards and 

 a little inwards. It also assists in extending the distal phalanx. 



The muscle rests upon the opponens pollicis, and the superficial 

 head of the flexor brevis pollicis hes on its inner side. 



2. Opponens Pollicis — Origin. — (i) The front of the anterior 

 annular ligament, and (2) the tuberosity of the trapezium. 



Insertion. — ^The outer border of the shaft of the metacarpal bone 

 of the thumb, and the adjacent part of its palmar surface. 



Nerve-supply. — ^The median ner\-e. 



The muscle, which is triangular, is directed downwards and 

 outwards. 



Action. — ^To flex the first metacarpal bone, the result being that 

 the thumb is drawn forwards and inwards across the palm, so as to 

 oppose its tip to the tips of the four inner fingers. 



