500 



THE MUSCULATURE 



Relations. — The interosseous muscles are covered on the plantar surface by a thin fascia 

 on which the deep branches of the lateral plantar nerve and vessels run. The first dorsal inter- 

 osseous adjoins medially the flexor hallucis brevis and laterally on the plantar surface of the 

 second metatarsal, adjoins the second dorsal interosseous. Dorsal and plantar interossei then 

 alternate across the plantar surface of the foot until the fifth metatarsal is reached. Here the 

 third plantar interosseous adjoins the flexor brevis of the little toe. 



Fig. 422. — Fourth Layer of the Muscles of the Sole. 



Peroneus longus 



Plantar interossei 



Dorsal interossei 



Aclion.—T\\Q chief axis of the foot may be taken to extend through the second toe. The 

 dorsal interosseous muscles abduct — pull the digits to which they are attached away from this 

 axis; the plantar interosseous muscles adduct — pull the digits toward the axis. The interossei 

 all flex the first row of phalanges. 



Variations. — The second dorsal interosseous may have no attachment to the third 

 metatarsal. 



BURS^ 



B. intermetatarscphalangeae. — Four bursaj between the neighbouring sides of the heads of 

 the metatarsal bones and dorsal to the transverse capitular ligaments. B. mm. lumbricalium. 

 — Between the ends of the tendons of the lumbrical muscles and the transverse capitular liga- 

 ments. The tliree medial are more constant than the lateral. 



For other bursa; in the foot, see pp. 483 and 491. 



MUSCLES GROUPED ACCORDING TO FUNCTION 



The exact functions of many of the muscles have not yet been decisively determined. 

 Anatomical studios, the coiistrurtion of mechanical models, the electrical stimulation of the 

 musculature, and observation of tlic niu.scular activities of normal individuals and of individuals 

 in whom given muscles or sets of niu.scles are aljscnt or paralysed, have all proved valuable 

 methods of investigation, l)ut each method has its drawbacks, and knowledge of the part actu- 

 ally played by individual muscles in the normal activities of the body is as yet merely approxi- 



