THE REGION OF THE ANKLE AND FOOT 483 



diaphysis of the tibia, it is entirely extra-capsular and extra- 

 synovial (Fig. 143), and, on this account, the ankle-joint is 

 rarely involved. The disease commonly spreads along the 

 diaphysis, producing diffuse osteo-myelitis, or it may spread 

 towards the surface of the bone, perforate the periosteum, and 

 affect the soft parts. 



Tuberculous disease originating in the distal end of the 

 fibular diaphysis spreads in a precisely similar manner, but the 



Flexor hallucis 

 longus 



Pad of fat 



FIG. 144. Sagittal Section of Foot, showing some of the Articulations. 

 The synovial membranes are shown in red. 



1. Flexor hallucis longus. 



2. Plantar accessory :netatarso-phal- 



angeal ligament. 



3. Sesamoid bone. 



4. Flexor hallucis brevis. 



5. Plantar aponeurosis. 



6. Flexor digitorum brevis. 



7. Tibialis posterior tendon. 



8. Flexor digitorum longus tendon. 



9. Plantar calcaneo - navicular liga- 



ment. 



10. Quadratus plantae. 



11. Lateral plantar vessels and nerve. 



12. Calcaneus. 



ankle-joint may be infected when the fibular diaphysis is 

 intra-capsular (p. 481). 



When the disease commences in the neck of the talus, it may 

 spread (i) upwards, when it at once involves the synovial 

 membrane of the ankle-joint ; (2) backwards, so as to infect 

 the body of the bone, whence it spreads through the articular 

 cartilage, either upwards to the ankle-joint or downwards to 

 the talo-calcanean joint ; (3) forwards, so as to infect the talo- 

 calcaneo-navicular joint (Fig. 144). 



The Joints of the Foot. The Talo-Calcanean Joint 

 lies immediately below the ankle-joint and possesses a separate 



31 a 



