DISSECTION OF THE LOWER EXTREMITY 169 



leg muscles to locomotion. The relative atrophy of the motor system of 

 the toes is due to the loss of its femoral attachment and to a displacement 

 of the flexors and extensors, deprived of their tibial and fibular attach- 

 ments, downward into the intrinsic musculature of the foot. The pro- 

 nator and supinator systems are almost absent, being represented by the 

 popliteus alone, and this through skeletal modifications has lost its primi- 

 tive role. The muscles of the leg, like those of the forearm, are delimited 

 into an anterior, a posterior, and a lateral group by the bones of the leg 

 and aponeurotic septa. 



Study carefully the origin, insertion, form, action, and inner- 

 vation of the following muscles : 



(a) Triceps muscle of the calf (M. triceps surae). (Vide Spalteholz, 



Figs. 393-94.) 



(aa) Gastrocnemius muscle (M. gastrocnemius) . 



(aaa) Lateral head (caput laterale). Look for a small 



sesamoid cartilage or bone in this head. Observe 

 the lateral bursa of the gastrocnemius (bursa M. 

 gastrocnemii lateralis) and the bursa bicipitogas- 

 trocnemialis. 



(aab) Medial head (caput mediale). Observe the medial 



bursa of the gastrocnemius (bursa M. gastrocnemii 

 medialis) and the bursa M. semimembranosi. Dis- 

 sect this bursa out carefully and determine whether 

 or not it communicates with the joint-cavity. 

 Divide the gastrocnemius transversely near its attachment to 

 the tendo Achillis and reflect it upward, preserving vessels and 

 nerves passing into each head, and study the muscle beneath the 

 M. gastrocnemius. 



(ab) Soleus muscle (M. soleus). (Vide Spalteholz, Fig. 394.) 



'Determine its exact origin from the fibula and 

 tibia. Note that the tendon of this muscle fuses 

 with the tendon of the gastrocnemius to form 

 the 

 (aba) Tendo calcaneus [Achillis]. 



Divide the soleus transversely at the level at 

 which it joins the gastrocnemius. Incise the belly 

 of the soleus in the middle line and expose the 

 tendinous arch (arcus tendineus M. solei) and the 

 blood-vessels and nerves entering the muscle. 

 The plantaris muscle may be divided to permit of 

 the turning of the tendo calcaneus [Achillis] 

 downward. Determine its exact attachment to the 

 os calcaneum and study the following bursae : 



(1) Bursa subcutanea calcanea. (Vide Spalte- 



holz, Fig. 393.) 



(2) Bursa tendinis calcanea. (Vide Spalteholz, 



Fig. 395.) 



(b) Plantaris muscle (M. plantaris). (Vide SpaKaholz, Ffe. J 



tendon of this small muscle has already been divided to P-n 



