40 LABORATORY DIRECTIONS 



femorls so as to swing the leg forward until the toe points towards 

 the head. The large, flat, triangular obturator externus muscle 

 should now be exposed. It originates on the medial border of 

 the obturator foramen and inserts in the trochanteric fossa. 

 Action: to rotate the thigh. 



Muscles of the Shank and of the Foot 



Skin the foot and remove all superficial fascia from both 

 shank and foot. This will involve removal of the insertions of 

 some of the thigh muscles. From now on it is important, at the 

 end of each laboratory period, to wrap the shank and foot with 

 cheese cloth soaked in embalming fluid, to prevent the muscles 

 from becoming dry. 



Most of the muscles of the shank extend onto the foot; their 

 tendons should be traced to the points of insertion. 



24. Gastrocnemius. — Almost all of the mass of muscle 

 forming the calf of the leg is the gastrocnemius, composed of two 

 heads, a caput mediale (medial head) and a caput laterale (lateral 

 head). Between the caput mediale and caput laterale lies 

 another muscle, the plantaris. With the handle of a scalpel 

 separate the muscles, beginning in the depression behind the 

 knee. The caput mediale will separate easily; the caput laterale 

 will be difficult to separate from the plantaris. The two heads 

 of the gastrocnemius unite about one-third the way down the 

 shank. The caput laterale originates from four places: from 

 superficial fascia of the shank, from the lateral edge of the 

 patella, from a sesamoid bone on the lateral side of the head of 

 the tibia, and from an aponeurosis covering the plantaris. The 

 caput mediale originates from the distal end of the femur and 

 from a sesamoid bone on the medial side of the head of the tibia. 

 The tendons of the two heads of the gastrocnemius and of 

 another muscle, the soleus, unite to form the large tendo7i of 

 Achilles^ which inserts on the calcaneus bone. 



Action: to extend the foot. 



25. Plantaris. — Dissection of the gastrocnemius has already 

 revealed this muscle. It originates by a tendon (which it shares 

 with the caput laterale) from the lateral edge of the patella, 

 and from the sesamoid bone on the lateral side of the head of the 

 tibia. The tendon of the plantaris forms the core of the tendon 



