248 MYOLOGY. 



Posterior Tibial Group. 



For convenience of description, we subdivide the muscles of this 

 group, but the subdivision is a somewhat artificial one, as some 

 of the muscles have two actions, flexing one joint and extending 

 another. 



Extensors. 



Gastrocnemius. 

 Plantaris. 



Flexors. 



Flexor pedis perfoi'atus. 

 Flexor pedis perforans. 

 Flexor pedis accessorius. 

 Popliteus. 



GASTROCNEMIUS. 



(Bifemoro-calcaneus.) 

 (Pl. IIL 38.) 



Situated at the back of the leg, this muscle is somew^hat heart- 

 shaped, ending in a flattened tendon ; the flesh}^ belly is divisible 

 into two portions, and intersected superiorly by strong tendons. 



Origin. — By two heads ; one from a ridge extending upwards 

 from the external condyle in front of the supracondjdoid fossa ; 

 the other from the posterior surface of the femur, just above the 

 intercondyloid fossa, and from the internal condvle. 



Insertion. — To the posterior jDart of the summit of the 

 calcaneum, a synovial bursa being interposed between it and the 

 anterior part, over which it passes. 



Relation. — Anteriorly with the flexor perforatus, popliteus, 

 popliteal vessels and nerves, and the vastus externus above ; 

 posteriorly with the triceps abductor femoris ; internally with 

 biceps rotator tibialis ; superficially with the tibial fascia ; 

 inferiorly the tendon is covered by that of the flexor perforatus, 

 the two forming the Tendo-Achillis. 



Action. — To extend the tarsal joint. 



