THE MUSCLES OF THE HAND. 



289 



metacarpal bone, and between these heads there is left superiorly an interval wider 

 than in the other dorsal interosseous muscles. 



Relations. Between the heads of the abductor indicis the radial artery passes forwards to 

 the palm of the hand ; between those of the other dorsal interosseous muscles small perforat- 

 ing arterial branches are transmitted. 



The three palmar interosseous muscles are adductors, drawing the index, 

 ring, and little fingers towards the middle line of the hand. They are visible only 

 on the palmar aspect of the hand, each one arising from the corresponding lateral 

 surface of the body of the metacarpal bone of the finger on which It acts : they 

 terminate, like the dorsal muscles, in small tendons inserted partly into the bases 

 of the first phalanges at the side, and partly into the extensor tendons. The first 

 palmar interosseous muscle belongs to the ulnar side of the index finger ; the others, 

 are placed on the radial sides of the ring and little fingers. 



Fig. 246. THE RIGHT HAND FROM BEHIND, SHOWING THE DORSAL INTEROSSEOUS MUSCLES. (R. Quain.) * 



The tendons of the extensor muscles Lave been removed as far as the distal ends of the metacarpal 

 bones. 1, 2, 3, and 4, the dorsal interosseous muscles, in order from the radial side inwards ; their ex- 

 panded insertion in connection with the extensor tendons, is shown upon the first phalanges. 



Fig. 247. THE RIGHT HAND FROM BEFORE, SHOWING THE PALMAR INTEROSSEOUS MUSCLES. 



(R. Quain.) f 



1, 2, 3, refer to the first, second, and third palmar interosseous muscles. 



Small bursse are often present between the tendons of the interosseous muscles and the 

 metacarpo-phalangeal articulations, as. well as in the interspaces between the heads of the 

 inner four metacarpal bones. 



Varieties of the short muscles of the hand. The palmaris brevis varies greatly in 

 the strength of its muscular fibres, and somewhat also in their length and direction. It is 

 seldom entirely absent. It is sometimes found running into the flexor minimi digiti. 



The abductor pollicis is often divided into an outer and an inner part a condition described 

 by Scemmerring as normal. Accessory slips are also found joining the muscle, frequently 

 from the tendon of the extensor ossis metacarpi pollicis or palmaris longus, more rarely from 

 the extensor carpi radialis longior (or accessorius), from the styloid process or opponens pollicis. 

 Another slip, which is frequently present, springs from the skin over the upper part of the 

 thenar eminence. 



The deep head of the flexor brevis pollicis is sometimes wanting. On the other hand it 

 may be larger than usual, and arise in part from the upper end of the second metacarpal 

 bone. 



The two adductors vary in their relative extent and in the closeness of their connection. 

 The adductor obliquus sometimes receives a slip from the transverse metacarpal ligament. 



