THE LOWER LIMB 



557 



long extensor only) on the dorsal aspects of the first phalanges of 

 the same toes. 



Dorsal Interossei.— These belong to the second, third, and fourth 

 toes, the second toe having two. They are named first, second, 

 third, and fourth, from within outwards. 



Origin. — Each muscle arises by two heads from the adjacent lateral 

 surfaces of the shafts of the metatarsal bones between which it is 

 situated, but more extensively from the metatarsal bone of the toe 

 upon which the muscle acts than from the other bone. In the case 

 of the first (most internal) muscle its inner head is comparatively 

 small, and arises from the outer side of the base of the first meta- 

 tarsal bone, as weU as from the adjacent portion of the internal 

 cuneiform. 



Fig. 262. — The Interosseous Muscles of the Right Foot. 

 A, Plantar; B, Dorsal. 



Insertion. — ^The dorsal interossei are inserted in a manner pre- 

 cisely similar to the plantar interossei. The first and second dorsal 

 interossei belong to the second toe, one on either side ; the third 

 belongs to the outer side of the third toe ; and the fourth to the 

 outer side of the fourth toe. In the case of all the interosseous 

 muscles the insertion into a first phalanx is comparatively slight, 

 the chief insertion being into the expansion of the extensor tendon 

 on the dorsal aspect of the first phalanx. 



Nerve-supply. — The external plantar nerve in the following 

 manner : the deep division of the nerve usually supplies the inter- 

 osseous muscles, with the exception of the two which occupy the 

 fourth (most external) interosseous space, namely, the fourth 

 dorsal and third plantar. These two are usually supplied by the 

 outer digital branch of the superficial division of the external plantar 



