SHOULDER, ARM, FOREARM, AND HAND. 



163 



2. The flexor brevis pollicis, flexes first phalanx. 



3. The opponens pollicis, acts on metacarpal. 



4. The adductor pollicis, adducts the first phalanx. 



The abductor pollicis (Fig. iio)is easily isolated. Cut the same near its 

 insertion, and turn it aside so as to preserve the nerve-supply. (Figs. 109 and 

 114.) This muscle arises from the bone at the base of the thumb the os 

 trapezium and the annular ligament. It is inserted into the base of the thumb, 

 proximal phalanx. (Fig. 109.) 



The opponens pollicis is inserted into the whole length of the thumb meta- 

 carpal bone. (Fig. 109.) It arises from the os trapezium and annular ligament. 

 (Fig. 114.) 



Flexor carpi 

 ulnaris 



Pronator quadratus 



Abductor pollieis 



Outer head of flexor 

 brevis pollicis 



Inner head of flexor 



breyis pollieis (first 



division) 



Opponens pollicis 

 Inner head of flexor 



breyis pollicis (third 



division) 



Inner head of flexor 

 breyie pollicis (second 

 division) 



Adductor pollicis 



Dorsal interoaseous 



Third palmar 

 interosseoua 



Fourth dorsal 

 mterosseous 

 Second palmar iuterosseous 



First palmar interoaseous 

 Third dorsal intsrosseous 



Second dorsal interoaseous 



FIG. 114. THE PRONATOR QUADRATUS AND DEEP VIEW OF THE PALM. 



Tlie flexor brevis pollicis has two heads, and between these two heads lies the 

 tendon of the flexor longus pollicis muscle. The outer, or more superficial head 

 (Fig. 114), arises from the os trapezium and annular ligament, and is inserted 

 into the base of the first thumb phalanx on the outer side. (Fig. 109.) The 

 deep or inner head has two parts : (i) A small part that arises from the first 

 metacarpal bone ; (2) a large part that arises from the annular ligament, the os 

 magnum, and the second and third metacarpals. (Fig. 1 14.) 



This latter is described by some authors as the oblique part of the adductor 

 pollicis. The deep part of the flexor brevis is inserted into the base of the first 

 thumb phalanx on the inner side. 



