THE FOOT. 



Peroneus Tcrtius. This tendon descends in front of the external malleolus and 

 inserts into the upper surface of the fifth metatarsal bone near its base. 



The other muscles of the leg do not support the tarsal arch. In considering 

 the insertions of these tendons it will be seen that the tibialis anterior, peroneus 

 tertius, and peroneus brevis are practically inserted into the convexity of the tarsal 

 arch and tend to support it by pulling 

 it upward. The flexor longus hallucis 

 and flexor longus digitorum run longitu- 

 dinally beneath the arch and so directly 

 support it. The tibialis posterior and 

 peroneus longus, one from the inner and 

 the other from the outer side, meet and 

 cross on the sole of the foot, thus form- 

 ing a double sling immediately beneath 

 the arch on which it rests when those 

 muscles contract. 



If these muscles, on which the arch 

 directly relies for its support when sub- 

 jected to the strain of locomotion, are 

 unable to meet the demands made upon 

 them then the strain falls on the liga- 

 ments, and as these are intended for 

 static arid not dynamic purposes they 

 weaken and give way and the arch de- 

 scends. To cure such a condition over 

 use must be avoided and the strength of 

 the muscles is to be restored by exercise, 

 massage, electricity, etc. 



THE ACTION OF THE MUSCLES AS 

 FLEXORS AND EXTENSORS. 



Peroneus longus 

 Peroneus tertius 



Flexor brevis 

 digitorum 



The peroneus group of muscles 

 exert so little influence on flexion and 

 extension that in many cases they may 

 be ignored. The peroneus tertius flexes 

 the ankle, while the longus and brevis 

 extend it. The common movements of 

 the foot when great strength is not re- 

 quired are performed by the flexor and 

 extensor groups of muscles ; the muscles 

 of the calf are not so much for adding 

 to the kind of movements as to the 

 amount. The powerful calf muscles 

 have the function of aiding the body in 

 maintaining the upright posture and 

 especially in lifting and propelling it 

 forward in locomotion. When most of 

 the flexors and extensors are paralyzed 

 the foot hangs loose from the leg, the 

 so-called flail-foot. Weakness of the 

 flexor group (tibialis posterior, flexor 

 longus digitorum, and flexor longus hallucis) tends to favor a descent of the arch 

 with consequent pronation or eversion. Weakness of the extensors causes toe-drop 

 and inversion or supination. 



Paralysis of the calf muscles deprives the posterior pillar of the arch of its support 

 and the action of the flexors and extensors elevates the arch while the heel descends, 

 so that a condition of hollow foot is produced. 



Posterior tibial 



Anterior tibial 



Extensor longus 

 hallucis 



Extensor longus 

 digitorum 

 Peroneus brevis 



FIG. 587. The foot in an adducted or supinated position. 



