644 MAMMALIAN ANATOMY 



They are distinguished from one another by the differences in size ; 

 they decrease in the following order : the fourth, the third, the fifth, 

 and the second. When the base is held toward the student, with the 

 dorsal border uppermost, the concave side of the shaft is on the side to 

 which the bone belongs. 



The distal phalanges are known by their compressed shape and 

 by the presence of the claw or claw support. When the proximal 

 articular surface is held toward the student and the small palmar 

 surface downward, a slight emargination at the lower part of the side 

 of the articular surface is on the side to which the bone belongs. 



Ossification. The phalanges are developed from two centres, one 

 for the base and one for the shaft. 



Muscular Attachments. Proximal Phalanges. To the sides of 

 the base of the proximal phalanges, and to the sesamoid bones, are 

 attached the palmar interosseous muscles, that of the thumb being 

 known as the flexor brevis pollicis and that of the little finger as the 

 flexor brevis minimi digiti. The lumbrical muscles are attached by 

 fascia to the radial side of the shafts of the four fingers. In addition 

 insertion is given 



(1) By the phalanx of the thumb to the adductor pollicis, the 

 abductor pollicis, and the tendon of the extensor indicis, known as 

 the extensor internodli pollicis. 



(2) By the proximal phalanx of the second or index finger, on 

 the radial side of the base to the first dorsal interosseous, and on the 

 ulnar side to the adductor indicis. 



(3) By the proximal phalanx of the middle finger, on the radial 

 side of the base to the third dorsal interosseous, and on the ulnar 

 side to the fourth dorsal interosseous. 



(4) By the proximal phalanx of the fourth finger, on the ulnar 

 side of the base to the fourth dorsal interosseous. 



(5) By the proximal phalanx of the little finger, at the base, on 

 the radial side to the adductor minimi digiti, and on the ulnar side to 

 the abductor minimi digiti. 



Middle Phalanges. A tendon of the flexor sublimis digitorum is 

 inserted on the palmar side of the base of the middle phalanx ; the 

 general extensor tendon, including slips from the lumbrical and 

 interosseous muscles, ends in the fascia on the dorsal aspect. 



Distal Phalanges. On the palmar side is inserted the tendon of 



