346 MUSCLES AND FASCIA. 



The Flexor Longus Pollicis is situated on the fibular side of the leg, and is the most 

 superficial, and largest of the three next muscles. It arises from the lower two- 

 thirds of the internal surface of the shaft of the fibula, with the exception of an 

 inch below ; from the lower part of the interosseous membrane ; from an inter- 

 muscular septum between it and the Peronei, externally ; and from the fascia 

 covering the Tibialis posticus. The fibres pass obliquely downwards and back- 

 wards, and terminate round a tendon which occupies nearly the whole length of 

 the posterior surface of the muscle. This tendon passes through a groove on the 

 posterior surface of the tibia, external to that for the Tibialis posticus and Flexor 

 longus digitorum ; it then passes through another groove on the posterior extremity 

 of the astragalus, and along a third groove, beneath the tubercle of the os calcis, 

 into the sole of the foot, where it runs forwards between the two heads of the 

 Flexor brevis pollicis, and is inserted into the base of the last phalanx of the great 

 toe. The grooves in the astragalus and os calcis which contain the tendon -of the 

 muscle are converted by tendinous fibres into distinct canals, lined by synovial 

 membrane ; and as the tendon crosses the sole of the foot, it is connected to the 

 common flexor by a tendinous slip. 



Relations. By its superficial surface, with the Soleus and tendo Achillis, from 

 which it is separated by the deep fascia. By its deep surface, with the fibula, 

 Tibialis posticus, the peroneal vessels, the lower part of the interosseous mem- 

 brane, and the ankle-joint. By its outer border, with the Peronei. By its inner 

 border, with the Tibialis posticus, and Flexor longus digitorum. 



The Flexor Longus Digitorum, is situated on the tibial side of the leg. At its 

 origin, it is thin and pointed, but gradually increases in size as it descends. It 

 arises from the posterior surface of the shaft of the tibia, immediately below the 

 oblique line, to within three inches of its extremity, internal to the tibial origin 

 of the Tibialis posticus ; some fibres also arise from the intermuscular septum, 

 between it and the Tibialis posticus. The fibres terminate in a tendon, which 

 runs nearly the whole length of the posterior surface of the muscle. This tendon 

 passes, behind the inner malleolus, in a groove, common to it and the Tibialis 

 posticus, but separated from the latter by a fibrous septum ; each tendon being 

 contained in a special sheath lined by a separate synovial membrane. It then 

 passes, obliquely, forwards and outwards, beneath the arch of the os calcis, into the 

 sole of the foot, where, crossing beneath the tendon of the Flexor longus pollicis, 

 to which it is connected by a strong tendinous slip, it becomes expanded, is joined 

 by the Flexor accessorius, and finally divides into four tendons, which are in- 

 serted into the bases of the last phalanges of the four lesser toes, each tendon pass- 

 ing through a fissure in the tendon of the Flexor brevis digitorum, opposite the 

 middle of the first phalanges. 



Relations. In the leg. By its superficial surface, with the Soleus, and the pos- 

 terior vessels and nerve, from which it is separated by the deep fascia. By 

 its deep surface, with the tibia and Tibialis posticus. In the foot, it is covered by 

 the Abductor pollicis, and Flexor brevis digitorum, and crosses beneath the 

 Flexor longus pollicis. 



The Tibialis Posticus lies between the two preceding muscles, and is the most 

 deeply seated of all the muscles in the leg. It commences above, by two pointed 

 processes, separated by an angular interval, through which the anterior tibial 

 vessels pass forwards to the front of the leg. It arises from the posterior surface of 

 the interosseous membrane, its whole length, excepting its lowest part, from the 

 posterior surface of the shaft of the tibia, external to the Flexor longus digitorum, 

 between the commencement of the oblique line above, and the middle of the 

 external border of the bone below, and from the upper two-thirds of the inner 

 surface of the shaft of the'fibula ; some fibres also arise from the deep fascia, and 

 from the intermuscular septa, separating it from the adjacent muscles on each 

 side. This muscle, in the lower fourth of the leg, passes in front of the Flexor 

 longus digitorum, terminates in a tendon, which passes through a groove with it 

 behind the inner malleolus, but inclosed in a separate sheath, then passes through 



