THOKACIC LIMBS 643 



The palmar third of the distal surface is little more than a rounded, 

 straight border ; above this there projects from the centre the bony 

 claw-plate, surrounded by a deep cleft. When the lateral surfaces 

 of the bone are broken away, this cleft is seen to extend back to the 

 edges of the proximal surface. The claw-plate is thus seen to be the 

 real shaft of the bone, the lateral surfaces being the extended surfaces 

 of a projecting hood, or collar. 



The claw-plate itself has the shape of a thin, curved triangle, the 

 apex whereof points distally, and, when the phalanx is held with its 

 proximal surface vertical, points also downward. In the position of 

 rest, the distal phalanx is retracted against the ulnar side of the 

 middle phalanx. The proximal surface then faces proximally, and is 

 the palmar aspect ; owing to the obliquity of the head of the middle 

 phalanx, the ulnar surface of the distal phalanx faces in a distal 

 direction as well as to the ulnar side. 



The terminal phalanges of the several digits present no important 

 points of difference. 



The claw is a thin, curved, triangular, horny case which fits closely 

 to the claw-plate ; the latter, however, does not extend into the tip of 

 the case. When the distal phalanx is retracted, the point of the claw 

 is proximal to the palmar end of the proximal surface, and therefore 

 no longer forms the end of the finger, and is useless. 



Determination. The proximal phalanges can be distinguished 

 from the other phalanges by their size, their deeply concave bases, 

 and their pulley-like distal ends. They can be distinguished from one 

 another by their relative size and by the greater or less curvature 

 toward the median line. Inasmuch as this curvature is directed 

 toward the median line, when a proximal phalanx is held with the 

 proximal end upward and the dorsal arched surface toward the student, 

 the concavity of the curvature will be on the side to which the bone 

 belongs if it be a fifth phalanx, and on the side opposite to that to 

 which the bone belongs if it be a second phalanx. The proximal 

 phalanx of the thumb is distinguished by its non-trochlear head. 

 When the proximal surface is held uppermost, the head transverse 

 and the dorsal surface toward the student, the articular surface on the 

 base points to the side to which the bone belongs. 



The middle phalanges can be distinguished by the prominence on 

 the dorsal end of the base and by the lateral position of the head. 



