EXTREMITIES. 41 



face concave, continue downwards and backwards to 

 the plantar cushion ; tlie superior border is thin and 

 flexible, the inferior thick and attached to the basilar 

 and retrossal processes; the posterior border is slightly 

 convex, the anterior is intimately united to the anterior 

 lateral ligament of the articulation of the foot. 

 Structure : is a mixture of fibrous and cartilaginous 

 tissue, liable to calcification. 



Plantar Cushion. — Is a wedge placed between the 

 cartilages of the os pedis, between the perforans ten- 

 don and the inferior wall of the horny box. It has 

 an antero-superior face covered by a cell ulo- fibrous 

 membrane, and is moulded on the aponeurotic termina- 

 tion of the perforans tendon ; its inf ero-posterior face 

 is covered by the keratogenous membrane and offers 

 in its middle the pyramidal body representing the 

 shape of the frog of tlie foot. The base looks back- 

 wards and upwards ; it shows on each side the bulbs of 

 the plantar cushion, and is also covered by a cellulo- 

 fibrous covering. The apex is fixed on the plantar 

 face of the os pedis, in front of the semilunai- crest 

 and the insertion of the perforans tendon. The la- 

 teral borders are continuous with the internal face of 

 tlie lateral cartilages. Its structure consists of a 

 fibrous network mixed with elastic fibres, connective 

 fibres with adipose cells, blood vessels and nerves. 



