THE LEG 341 



deep fascia with which they are continuous. Great care must 

 be taken not to injure the mucous sheaths of the tibialis anterior 

 and the extensor tendons of the toes, when the margins of the 

 transverse and cruciate ligaments are being defined, and whilst 

 the deep fascia is being reflected. They lie close to the deep surface 

 of the deep fascia. In the proximal part of the leg it will be 

 found impossible to raise the deep fascia from the subjacent 

 muscles without lacerating their surfaces. It should, therefore, 

 be left in position. At a more distal level it can readily be 

 separated. Divide it in a longitudinal direction midway between 

 the tibia and fibula. Turn the medial piece to the medial side, 

 until its attachment to the anterior border of the tibia is demon- 

 strated ; then turn the lateral piece to the lateral side, until its 

 continuity with the anterior fibular septum is displayed. 



After the medial and lateral attachments of the deep fascia 

 have been studied attempt to distend the synovial sheaths of 

 the tendons, either by inflation with a blow-pipe, or by the 

 injection of some fluid by means of a small syringe. Three 

 sheaths are to be examined; from the medial to the lateral side 

 they are, the sheath of the tibiaiis anterior, the sheath of the 

 extensor hallucis longus, and the sheath common to the extensor 

 digitorum longus and the peronaeus tertius (see Fig. 153, p. 342). 

 If the blow-pipe is used make a small incision through the 

 deep fascia of the foot into each sheath in turn, either between 

 the two bands of the cruciate ligament or beyond the lower 

 border of the cruciate ligament, and if a syringe is used insert 

 the needle into the sheaths in the same regions. If inflation 

 or injection fails, the positions and extents of the sheaths can be 

 fairly satisfactorily demonstrated by the use of a blunt probe, 

 introduced into the cavities of the sheaths through the openings 

 made through their boundaries. 



The Mucous Sheaths on the Dorsum of the Foot. Three 

 mucous sheaths are found in the region of the front of the 

 ankle and on the dorsum of the foot one round the tendon 

 of the tibialis anterior, the second round the tendon of the 

 extensor hallucis longus, and the third encloses the tendons 

 of the extensor digitorirm longus and the peronaeus tertius. 

 The first extends from the proximal border of the transverse 

 ligament to within a short distance of the insertion of the 

 tibialis anterior into the medial side of the first cuneiform 

 bone. The second extends from behind the lower part of 

 the transverse ligament to the first phalanx of the great toe ; 

 and the limits of the third are the lower border of the 

 transverse ligament, proximally, and the middle of the 

 dorsum of the foot distally. The sheaths facilitate the 

 movements of the tendons behind the ligaments when the 

 muscles are in action, and they are of surgical importance 

 because they are liable to become inflamed. 



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