OF THE FOOT. 349 



ens ; one externally, for the tendons of the Extensor longus digitorum and Pero- 

 neus tertius, and the tendon of the Extensor proprius pollicis, and the anterior tibial 

 vessels and nerve pass beneath it. The horizontal portion is attached externally 

 to the upper surface of the os calcis, in front of the depression for the interosseous 

 ligament, and internally to the inner malleolus and plantar fascia : it contains 

 three sheaths, the most internal for the tendon of the Tibialis anticus, the next 

 in order for the tendon of the Extensor proprius pollicis, and the most external for 

 the Extensor communis digitorum and Peroneus tertius : the anterior tibial ves- 

 sels and nerve lie altogether beneath it. These sheaths are lined by separate 

 synovial membranes. 



The Internal Annular Ligament is a strong fibrous band, which extends from 

 the inner malleolus above, to the internal margin of the os calcis below, converting 

 a series of bony grooves in this situation into osteo-fibrous canals, for the passage 

 of the tendons of the Flexor muscles and vessels into the sole of the foot. It is 

 continuous above with the deep fascia of the leg, below with the plantar fascia 

 and the fibres of origin of the Abductor pollicis muscle. The three canals which 

 it forms transmit from within outwards, first, the tendon of the Tibialis posticue ; 

 secondly, the tendon of the Flexor longus digitorum, then the posterior tibial vessels 

 and nerve, which run through a broad space beneath the ligament ; lastly, in a 

 canal formed partly by the astragalus, the tendon of the Flexor longus pollicis. 

 Each of these canals is lined by a separate synovial membrane. 



The External Annular Ligament extends from the extremity of the t>uter 

 malleolus to the outer surface of the os calcis, and binds down the tendons of the 

 Peronei muscles in their passage beneath the outer ankle. The two tendons are 

 inclosed in one synovial sac. 



Dissection of the Sole of the Foot. The foot should be placed on a high block with the sole 

 uppermost, and firmly secured in that position. Carry an incision round the heel and along the 

 inner and outer borders of the foot to the great and little toes. This incision should divide the 

 integument and thick layer of granular fat beneath, until the fascia is visible ; it should then be 

 removed from the fascia in a direction from behind forwards, as seen in fig. 189. 



The Plantar Fascia, the densest of all the fibrous membranes, is of great 

 strength, and consists of dense pearly -white glistening fibres, disposed, for the 

 most part, longitudinally ; it is divided into a central and two lateral portions. 



The central portion, the thickest, is narrow behind and attached to the inner 

 tuberosity of the os calcis, behind the origin of the Flexor brevis digitorum, and, 

 becoming broader and thinner in front, divides opposite the middle of the meta- 

 tarsal bones into five processes, one for each of the toes. Each of these processes 

 divides opposite the metatarso-phalangeal articulation into two slips, which em- 

 brace the sides of the Flexor tendons of the toes, and are inserted into the sides 

 of the metatarsal bones, and into the transverse metatarsal ligament, thus forming 

 a series of arches through which the tendons of the short and long Flexors pass to 

 the toes. The intervals left between the five processes allow the digital vessels 

 and nerves, and the tendons of the Lumbricales and Interossei muscles to become 

 superficial. At the point of division of the fascia into processes and slips, 

 numerous transverse fibres are superadded, which serve to increase the strength 

 of the fascia at this part, by binding the processes together and connecting them 

 with the integument. The central portion of the plantar fascia is continuous with 

 the lateral portions at each side, and sends upwards into the foot, at their point 

 of junction, two strong vertical intermuscular septa, broader in front than behind, 

 which separate the middle from the external amd internal plantar group of muscles ; 

 from these, again, thinner transverse septa are derived, which separate the various 

 layers of muscles in this region. The upper surface of this fascia gives attach- 

 ment behind to the Flexor brevis digitorum muscle. 



The lateral portions of the plantar fascia are thinner than the central piece and 

 cover the sides of the foot. 



The outer portion covers the under surface of the Abductor minimi digiti ; it Ls 



