THE ANTERIOR TIBIOFIBULAR REGION 231 



for the peroneus tertius and extensor longus, one for the extensor 

 proprius hallucis, and one for the tibialis anticus; may be a 

 bursa between the fundiform ligament and neck of the 

 astragalus. 



Internal annular ligament (ligamentum laciniatum, p. n.) 

 covers the flexor tendons, completing canals; it is attached 

 to the inner malleolus and posteriorly to the inner side of the 

 os calcis. 



The external annular ligament (retinaculum peronasorum 

 superius, p. n.) forms sheaths for the long and short peroneal 

 tendons, passing from the outer malleolus to the os calcis. 

 May be subcutaneous bursae over the malleoli and over the 

 lower end of the tendo Achillis. 



The Anterior Tibiofibular Region (Extensors) 



1. M. Tibialis Anticus ("chain-muscle"). Origin, external 

 tuberosity of the tibia, upper half of the outer surface of that 

 bone, and adjacent interosseous membrane, fascia of the leg, 

 and intermuscular septum; insertion, oval mark on the inner 

 and lower part of the internal cuneiform and first metatarsal, 

 dividing into two slips. A small bursa may be under its near 

 insertion. 



A part may be inserted into the astragalus, also a slip may 

 go to the head of the first metatarsal or base of first phalanx. 



2. M. Extensor Longus or Proprius Hallucis. Origin, middle 

 two-fourths of the narrow anterior surface of the fibula and 

 contiguous portion of the interosseous membrane; insertion, 

 base of the terminal phalanx of the great toe on the dorsal 

 aspect. It spreads in an expansion on each side over the meta- 

 tarsophalangeal articulation, and almost always sends a slip 

 to the base of the proximal phalanx. 



3. M. Extensor Longus Digitorum Pedis. Origin, external 

 tuberosity of the tibia, head and upper two-thirds of the 

 anterior surface of the fibula, very largely from the septa 

 and fascia and interosseous membrane above the origin of 

 the extensor proprius hallucis. Tendon divides into four slips 

 for the outer four toes. They are continued into expansions 

 which are joined on the proximal phalanx by processes from 

 the interossei and lumbricales. They divide into three parts 

 the middle inserted into the middle phalanx; the lateral parts 



