424 MUSCLES AND FASCIAE. 



tibia, external to that for the Tibialis Posticus and Flexor Longus Digitorum ; 

 it then passes through another groove on the posterior extremity of the astra- 

 galus, 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 con- 

 nected to the common flexor by a tendinous slip. 



Relations. By its sujjerficial 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 interosseus 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 (Perforans) 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, imme- 

 diately 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 termi- 

 nate 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 (Fig. 262), where, 

 crossing beneath the tendon of the Flexor Longus Pollicis, to which it is con- 

 nected by a strong tendinous slip, it becomes expanded, is joined by the Flexor 

 Accessorius, and finally divides into four tendons which are inserted into tho 

 bases of the last phalanges of the four lesser toes, each tendon passing 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 tibial 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 Poslicus 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 whole of the 

 posterior surface of the interosseous membrane, 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 behind the inner malleolus, with the tendon of that muscle, 

 but inclosed in a separate sheath ; it then passes through another sheath, over 

 the internal lateral ligament, and beneath the calcaneo-scaphoid articulation, 

 and is inserted into the tuberosity of the scaphoid, and internal cuneiform bones. 

 The tendon of this muscle contains a sesamoid bone, near its insertion, and gives 

 off' fibrous expansions, one of which passes backwards to the os calcis, others 

 outwards to the middle and external cuneiform, and some forwards to the bases 

 of the third and fourth metatarsal bones (Fig. 263). 



