THE HAND. 



355 



palm is hollow, with a muscular mass on each side. That on the thumb side is 

 called the thenar eminence ; it is formed by the abductor, opponens, and outer head 

 of the flexor brevis pollicis. The prominence on the ulnar side of the hand is called 

 the hypothenar eminence and is formed by the abductor, opponens, and flexor brevis 

 minimi digiti. The palmaris brevis muscle overlies them transversely. The palm is 

 marked by four creases, two longitudinal and two transverse. One longitudinal 

 crease begins at the middle of the wrist between the thenar and hypothenar emi- 

 nences to end on the radial side of the index finger, opposite the head of its meta- 

 carpal bone. It is caused by adduction of the thumb. The other longitudinal crease 

 runs somewhat parallel to the first, starting near the wrist and ending in the web 



Abductor pollicis 



Opponens pollicis 



Flexor brevis pollicis 



Adductor pollicis, 

 oblique portion 



Adductor pollicis, 

 transverse portion 



Abductor minimi digiti 



Opponens minimi digiti 



Flexor brevis minimi 

 digiti 



Interossei muscles 



FIG. 368. Muscles of the hand. 



between the index and middle fingers. It is formed by hollowing the hand. The 

 upper transverse crease begins on the radial side of the index finger where the first 

 longitudinal crease ends, and runs obliquely across the palm to the middle of the 

 hypothenar eminence. It is formed by the flexion of the fingers, especially the 

 index, and where it crosses a line drawn through the middle of the midd 1 > finger 

 marks the lowest point of the superficial palmar arch. The position of the lowest 

 portion of the superficial palmar arch is also indicated by a line drawn across the palm 

 opposite to the web of the thumb and index finger. The lower transverse crease 

 begins on the hypothenar eminence opposite the head of the fifth metacarpal bone 

 and is formed by the flexion of the middle, ring, and especially the little finger. 

 When it reaches the vicinity of the median line it merges with the second longi- 



