MUSCLES OF THE POSTERIOR LIMBS. 305 



Situation Direction Form Structure. Situated behind the tibia, 

 below the femoro-tibial articulation, this muscle is oblique downwards and 

 inwards, short and triangular, tendinous at its supero-external angle, and 

 formed, for the remainder of its extent, of divergent fleshy fibres, the longest 

 of which are the most inferior. 



Attachments. 1. In the lowest of the two fossae excavated on the outside 

 of the external condyle of the femur, by its tendon origin. 2. On the 

 supero-posterior triangular surface of the body of the tibia, by the inferior 

 extremity of its muscular fibres termination. 



Eelations. Posteriorly, with the gastrocnemii and the perforatus. In 

 front, with the posterior ligament of the femoro-tibial articulation, and the 

 popliteal vessels. Outwards, with the oblique and deep flexors of the 

 phalanges. Inwards, with the semitendinosus and tibial aponeurosis. The 

 tendon, concealed at its origin beneath the external femoro-tibial ligament, 

 glides, by its deep face, over the contour of the external semilunar cartilage 

 and the posterior portion of the external facet on the tibia. 



Action. It flexes the tibia, and gives it a slight rotatory movement out- 

 wards. 



5. Deep Flexor of the Phalanges or Perforans. (Figs. 135, 23 ; 137, 23.) 



Synonyms. Tibio-phalangeus Girard. The flexor perforans and flexor longus 

 pollicis pedis of Man. (Flexor pedisPercicall. Great tibio-plialangeusLryh.) 



Extent Situation Direction Composition. Extending from the supe- 

 rior extremity of the leg to the third phalanx, and situated behind the tibia 

 and foot, whose direction it follows, this muscle is composed of a muscular 

 body and a tendon. 



Form, Structure, and Attachments of the muscular portion. This is thick 

 and prismatic, and incompletely divided into two portions an internal, 1 

 and an external, 2 which is the most voluminous. It is attached : 1, To the 

 posterior face of the tibia, on the linear imprints which occupy the inferior 

 triangular surface ; 2, To the supero-external tuberosity of the same bone ; 

 3, To the peroneus ; 4, To the interosseous ligament uniting that bone to 

 the tibia. 



Direction and Attachments of the tendon. The tendon commences above 

 the inferior extremity of the tibia, where it is most usually double, each 

 muscular portion being succeeded by a tendinous cord whose volume is in 

 harmony with the size of the muscle from which it proceeds. The single 

 tendon resulting from the union of these two primary ones enters the groove 

 formed by the inner face of the os calcis, where it is retained by a fibrous 

 arch which transforms this channel into a perfect sheath, designated the 

 tarsal sheath; it glides in the interior of this canal by means of a very 

 extensive vaginal synovial membrane, which extends upwards on the 

 posterior ligament of the tibio-tarsal articulation, and is prolonged inferiorly 

 to the middle third of the metatarsal region. The tendon of the perforans 

 afterwards descends vertically behind the suspensory ligament, receiving 

 from it a strong fibrous band analogous to that of the fore-limb, but less 

 voluminous ; it then passes through the annular portion of the perforatus, 

 is inflected with that muscle over the great sesamoid groove, glides on the 

 posterior articulating surface of the second phalanx and that on the small 

 sesamoid bone, thinning out into a plantar aponeurosis which is provided with 



1 The tibialis posticus of Man. 2 The flexor longus pollicis of Man. 



