S 68 APPLIED ANATOMY. 



THE MUSCLES OF THE FOOT. 



The foot is acted upon by long muscles which come down from the leg and 

 short muscles which arise in the foot itself. Of these the long muscles are the more 

 important because they influence the position of the foot itself, whereas the short 

 muscles act on the toes ; as stated the movements of the toes are of secondary impor- 

 tance (page 562). The functions of the muscles are active or dynamic in character. 

 They bear the weight of the body when in motion and direct the movements of the 

 foot in locomotion. Their function and structure are to be studied together, as one 

 explains the other, and a knowledge of them explains many deformities and indicates 

 their treatment. 



The long muscles have three distinct actions on the foot: (i) they support the 

 arch of the foot; (2) they flex and extend the foot; (3) they abduct and adduct the 

 foot this latter being associated with a certain amount of rotation. 



The action of the individual muscles is not a simple one. They act on two 

 joints, the ankle and subastragaloid. If the former is stationary they abduct and 

 adduct, if the latter is stationary they flex and extend, but if both move then a com- 

 bined action of the muscles is necessary. 



For our purposes we may divide the muscles into four groups of three each 

 (page 546). They are (i) extensors, (2) flexors, (3) abductors, (4) muscles of 

 the calf. 



1 . Extensor group : tibialis anterior, extensor longus hallucis, extensor longus 

 digitorum. 



2. Flexor group: tibialis posterior ; flexor longus digitorum, flexor longus 

 hallucis. 



3. Abductor group : peroneus longus, peroneus brevis, peroneus tertius. 



4. Muscles of the calf: gastrocnemius, soleus, plantaris. 



THE ACTION OF THE MUSCLES IN SUPPORTING THE TARSAL ARCH. 



Tibialis Anterior. The tendon of the anterior tibial descends along the anterior 

 edge of the internal malleolus and inserts into the lower inner surface of the internal 

 cuneiform bone and base of the first metatarsal bone. 



Tibialis Posterior. Its tendon passes down close behind the posterior edge of 

 the internal malleolus, crosses the internal lateral ligament of the ankle, passes 

 under the inferior calcaneonavicular (scaphoid) ligament and in front of the susten- 

 taculum tali to insert into the tubercle of the navicular (scaphoid). From the tuber- 

 cle its tendon sends slips to all the tarsal bones except the talus (astragalus) and to 

 the bases of the second, third, fourth, and sometimes fifth metatarsal bones. 



Flexor Longus Digitorum. Its tendon passes behind the internal malleolus 

 immediately posterior to the tibialis posterior and then curves around the susten- 

 taculum tali to enter the foot, passing forward to insert into the base of the terminal 

 phalanges of the outer four toes. 



Flexor Longus Hallucis. This tendon descends across the middle of the pos- 

 terior part of the ankle-joint and curves forward under the sustentaculum tali. It is 

 the most posterior of the structures running behind the internal malleolus. It lies 

 deeper than the tendon of the flexor longus digitorum, and as it crosses it gives to it 

 a small slip. It then inserts into the base of the terminal phalanx of the big toe. 



Peroneus Longus. This tendon overlies the tendon of the peroneus brevis as 

 it passes down immediately behind the external malleolus. It then winds around 

 the outer surface of the os calcis behind the peroneal tubercle to pass obliquely 

 inward and forward across the sole of the foot, in a canal formed by the long plantar 

 ligament and a groove in the cuboid bone, to insert into the base of the first meta- 

 tarsal bone and internal cuneiform. 



Peroneus Brevis. This tendon passes down behind the external malleolus 

 beneath and a little anterior to the tendon of the peroneus longus. It passes in front 

 of the peroneal tubercle and then goes forward to insert into the tuberosity of the 

 fifth metatarsal bone. 



