FASCIAE OF THE FOOT. 427 



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 Longus Digitorum and Peroneus Tertius: the anterior tibial vessels 

 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, con- 

 verting a series of bony grooves in this situation into osseo-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 Posticus ; second, 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 syno- 

 vial membrane. 



The External Annular Ligament extends from the extremity of the outer 

 malleolus to the outer surface of the os calcis ; it 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 alon^ 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 ; the skin and fat 

 should then be removed from the fascia in a direction from behind forwards, as seen in Fig. 256. 



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 

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

 processes divides opposite the metatarso-phalangeal articulation into two slips, 

 which embrace 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 to- 

 gether, 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 intermus- 

 cular septa, broader in front than behind, which separate the middle from the 

 external and internal plantar group of muscles; from these again thinner trans- 

 verse septa are derived, which separate the various layers of muscles in this 

 region. The upper surface of this fascia gives .attachment 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 

 is thick behind, thin in front, and extends from the os calcis forwards to the 

 base of the fifth metatarsal bone, into the outer side of which it is .attached ; it 

 is continuous internally with the middle portion of the plantar fascia, and 

 externally with the dorsal fascia. 



