THE REGION OF THE ANKLE AND FOOT 479 



should be remembered that the tuberosity projects in a backward 

 direction, and that, on this account, in disarticulations (Key's 

 and Lisfranc's) at the tarso-metatarsal joint the knife, entered 

 on the lateral side, must be carried forwards and medially. 



When the ankle is actively flexed with the toes extended 

 (dorsi-flexed), the tendons of the extensor longus digitorwn and 

 halluds are rendered very prominent, as the skin and superficial 

 fascia on the dorsum of the foot are thin and the deep fascia is 

 not specially thickened except in certain situations. When the 



Navicular tuberosity 

 First metatarso-cuneiform joint 



FIG. 141. The Surface Landmarks on the Medial Side of the Ankle 

 and Foot. 



flexed foot is actively inverted, the tendon of the tibialis anterior 

 can be traced downwards across the medial part of the anterior 

 surface of the ankle-joint to its insertion into the first metatarsal 

 and the adjoining cuneiform bone (p. 469) on the medial side 

 of the foot. 



The sustentaculum tali lies one finger's breadth below the 

 medial malleolus, and it is slightly obscured by the flexor 

 digitorum longus tendon, which crosses its medial aspect. The 

 tendon of the flexor hallucis longus grooves the plantar surface 

 of the sustentaculum. The tuberosity of the navicular lies rather 

 more than one inch in front of the sustentaculum tali, and the 

 interval between the two is occupied by the head of the talus 

 (astragalus). This interval is increased in flat-foot by the 



