3 o8 APPLIED ANATOMY. 



2. The flexor sublimis digitorum arises from the medial (internal) condyle of 

 the humerus, the coronoid process, the intermuscular septa, and the oblique line of 

 the radius and divides into four tendons which split in front of the proximal pha- 

 langes to allow the profundus to pass through and then unite again and insert into 

 the sides of the middle phalanges. There are only four instead of five slips, because 

 the thumb has no middle phalanx but only proximal and distal ones (Fig. 323). 



3. The palmaris longus arises from the medial (internal) condyle of the 

 humerus and intermuscular septa and inserts into the palmar fascia, which is attached 

 to the base of the proximal phalanges, to the heads of the metacarpal bones, and 

 blends with the capsules of the metacarpophalangeal joints. It is thus seen to be a 

 perforated muscle exactly like the flexor sublimis, which it also resembles in func- 

 tion ; its attachment is not so far forward. Traction on it tends to flex the proximal 

 phalanx. 



THE EXTENSORS OF THE FINGERS. 



The extensors of the thumb and fingers arise from the lateral (external) condyle 

 and posterior surface of the ulna, radius, interosseous membrane, and intermuscular 

 septa. 



Three separate slips forming the extensor longus pollicis, extensor brevis 

 pollicis, and extensor ossis metacarpi pollicis go to the thumb. The longus 

 inserts into the distal phalanx, the brevis into the proximal, and the ossis into the 

 metacarpal bone of the thumb. 



The extensor communis digitorum divides into four slips, one for each 

 finger. The slip to the index is reinforced by an additional one called the exten- 

 sor indicis proprius muscle. The slip to the little finger is reinforced by the 

 extensor minimi digit! (ext. digit! quinti proprius) muscle. They divide 

 on the dorsum of the proximal phlanges into three parts, the middle one inserts into 

 the base of the middle phalanx, while the two lateral slips insert into the base of the 

 distal phalanx. 



2. THE FLEXORS AND EXTENSORS OF THE WRIST. 



The muscles which flex and extend the fingers of course also move the hand 

 as a whole, but in addition to these muscles there are five others, two flexor 

 muscles and three extensor muscles, which are inserted into the bones of the meta- 

 carpus and not into the phalanges. When these muscles contract they tend to 

 move the whole hand and not the fingers alone. They are the flexor carpi radialis, 

 flexor carpi ulnaris, extensor carpi radialis longior, extensor carpi radialis brevior, 

 and extensor carpi ulnaris. The palmaris longus has already been described as a 

 flexor of the fingers. 



FLEXORS OF THE WRIST. 



Flexor Carpi Radialis. The two flexors of the wrist, the flexor carpi 

 radialis and the flexor carpi ulnaris, are both superficial muscles lying directly 

 beneath the skin. The flexor carpi radialis arises from the medial (internal) 

 condyle of the humerus and intermuscular septa and lies between the pronator 

 radii teres externally and the palmaris longus internally. It runs obliquely across 

 the forearm, striking the wrist at about the junction of the middle and outer thirds. 

 It lies next to and to the outer side of the palmaris longus tendon and to the ulnar 

 side of the radial artery and inserts into the front of the base of the second meta- 

 carpal bone (Fig. 324). 



Flexor Carpi Ulnaris. The flexor carpi ulnaris arises by two heads, one 

 from the common tendon of the medial (internal) condyle and the other from 

 the olecranon process and upper two-thirds of the ulna. The two heads are 

 separated by the ulnar nerve, which passes down in the groove between the medial 

 condyle and olecranon process. The muscle passes straight down the anterior 

 and inner surface of the ulna to insert first into the pisiform bone and unciform 

 process and then to continue over to the base of the fifth metacarpal bone. The 

 pisiform bone is a sesamoid bone in the tendon of the flexor carpi ulnaris muscle. 



