200 FINGERS. 



The articulation of the upper end of this second bone would 

 seem calculated for motion in all directions ; yet, on account of 

 the strength of its lateral ligaments, the oblong figure of the joint 

 itself, and mobility of the first joint, it only allows flexion and 

 extension ; and these are generally much confined. 



The third bone of the thumb is the smallest, with a larse base, 



/ O * 



whose greatest extent is from oj?e side to the other. This base 

 is formed into two cavities and a middle protuberance, to be 

 adapted to the pulley of the former bone. This bone becomes 

 gradually smaller, till near the lower end, where it is a little 

 enlarged, and has an oval scabrous edge. Its body is rounded 

 behind, but is flatter than in the former bone, for sustaining the 

 nail. It is flat and rough before, by the insertion of the flexor 

 longus pollicis. 



The motion of this third bone is confined to flexion and 

 extension. 



The regular arrangement of the bones of the FINGERS in three 

 rows, has obtained for them the name of the three phalanges. 

 All of them have half round convex surfaces, covered with an 

 aponeurosis, formed by the tendons of the extensors, lumbri- 

 cales, and interossei, and placed directly backwards, for their 

 greater strength ; and their flat concave part is forwards, for 

 taking hold more surely, and for lodging the tendons of the 

 flexor muscles. The ligaments for keeping down these tendons 

 are fixed to the angles that are between the convex and concave 

 sides. 



The bones of the first phalanx of the fingers answer to the 

 description of the second bone of the thumb ; only that the 

 cavity in their base is not so oblong ; nor is their motion on the 

 metacarpal bones so much confined ; for they can move laterally 

 or circularly, the fore-finger in particular, but have no rotation, 

 or a very small degree of it, round their axis. 



The second bone of the fingers has its base formed into two 

 lateral cavities, and a middle protuberance : while the lower 

 end has two lateral protuberances, and a middle cavity : there- 

 fore, it is joined at both ends in the same manner ; which none 

 of the bones of the thumb are. 



