THE HAND. 



353 



point can travel without hindrance between all the carpal (with the exception of the 

 pisiform) and metacarpal bones. 



The phalangeal joints have two strong lateral ligaments and an anterior or 

 glenoid ligament, but no posterior ligament. 



Movements. While the amount of motion between the individual carpal 

 bones is limited to a slight gliding on one another, still, when taken together, a very 

 considerable range of movement is allowed. The hand can be flexed and extended, 

 abducted and adducted, and circumducted, but not rotated. If the bones of the 

 forearm at the wrist are held immovable it is impossible to rotate the hand. 



The radiocarpal joint bends more freely posteriorly (extension) than anteriorly, 

 while the midcarpal bends more freely in the opposite direction (Fig. 343, 344, p. 

 334), adduction (toward the ulnar side) is more extensive than abduction. The 

 movement between the two rows of carpal bones is quite extensive. 



The movements of the inner four carpometacarpal joints are both of flexion and 

 extension, mainly toward the palmar surface, and a lateral flexion and extension 

 which enables a person to ' ' hollow ' ' the 

 hand and so grasp round objects. The 

 palmar flexion of the fourth and fifth meta- 

 carpal bones is more marked than that of 

 the index and middle ones. The middle 

 metacarpal bone is the least movable. The 

 metacarpal bone of the thumb articulates 

 with the trapezium by a saddle-shaped joint 

 which allows flexion, extension, abduction, 

 adduction, and circumduction, but little or 

 no rotation. 



Abduction, adduction, and circumduc- 

 tion of the thumb occur at the carpometa- 

 carpal articulation and not at the metacar- 

 pophalangeal articulation. This latter is a 

 pure hinge-joint and possesses the move- 

 ments of flexion and extension only. 



The metacarpophalangeal articulations 

 of the fingers are practically saddle-shaped 

 joints resembling somewhat the ball-and- 

 socket joints with all their movements ex- 

 cept that of rotation. They can be flexed 

 to an angle of 90 degrees. The interpha- 

 langeal joints are hinge-joints and capable only of flexion and extension. The second 

 joint can be flexed to an angle of 150 degrees and the end joint to about a right angle. 



In flexion the distal phalanx always passes under the proximal bone, thus 

 causing the prominence of the knuckle to be formed by the proximal phalanx or 

 metacarpal bone (Fig. 366). 



FIG. 366. Showing how, when the fingers are 

 flexed, the prominence of the knuckles is formed by 

 the projection of the proximal bone. 



MUSCLES OF THE HAND. 



The hand contains not only the tendons of the long muscles which descend into 

 it from the forearm, but also some short muscles. They may be divided into three 

 sets, viz : a middle set, embracing the interossei and lumbricales ; an external set, 

 embracing the thumb muscles and forming the tJienar eminence ; and an internal 

 set, embracing the little finger muscles and forming the hypothenar eminence. 



The Middle Set. The interossei muscles arise from the adjacent sides of the 

 metacarpal bones; the lumbricales arise from the tendons of the flexor profundus digi- 

 torum. They all insert into the fibrous expansion of the long extensor tendons at the 

 sides of the proximal phalanges (Fig. 367). When they contract they flex the proximal 

 phalanx and extend the middle and distal phalanges. The interossei have a second 

 insertion into the sides of the base of the proximal phalanx. By their action the fingers 

 may be separated one from the other, or approximated. When the fingers are straight 

 the palmar interossei act as adductors, while the dorsal interossei act as abductors. 

 23 



