THE MUSCULAR SYSTEM. 163 



tion into the second phalanges, and the other two uniting to be 

 inserted into the bases of the third ; action, extends the phalanges 

 and, continuing, flexes the foot upon the leg ; nerve, the anterior 

 tibial. 



PERONEUS TERTIUS. Origin, from the lower front part of 

 the fibula on its outer side, from the interosseous membrane, and 

 the intermuscular septum between it and the peroneus brevis; 

 insertion, into the metatarsal bone of the little toe ; action, flexes 

 the tarsus upon the leg; nerve, the anterior tibial. 



Posterior Superficial Set. 



'GASTROCNEMIUS. Origin, from the upper and back part 

 of the external and internal condyles of the femur on either side, 

 above the origin of the popliteus, and from the supracondyloid 

 ridges; insertion, by joining with the tendon of the soleus to 

 form the tendo Achillis; action, extends the foot; nerve, from 

 the internal popliteal. 



SOLEUS. Origin, from the oblique line of the tibia, from 

 the middle third of the internal border, and from the posterior 

 surface of the head of the fibula ; insertion, by joining with the 

 tendon of the gastrocnemius to form the tendo Achillis; action, 

 extends the foot ; nerve, the internal popliteal. 



TENDO ACHILLIS. Origin, from the union of the gastroc- 

 nemius and soleus; is the largest and strongest tendon in the 

 body; it is inserted into the inferior surface of the posterior 

 tuberosity of the os calcis, having a synovial bursa between it 

 and the bone. 



PLANT ARIS. Origin, from the posterior ligament of the 

 knee-joint and the lower portion of the outer division of the 

 linea aspera ; insertion, into the posterior part of the os calcis to 

 the inner side of the tendo Achillis; action, the rudiment of a 

 muscle intended to render tense the plantar fascia; nerve, the 

 internal popliteal. 



Posterior Deep Set. 



POPLITEUS. Origin, from the outer side of the external con- 

 dyle, from the posterior ligament of the knee-joint; insertion, 

 above the oblique line on the posterior aspect of the shaft of the 

 tibia; action, assists in flexing the leg; nerve, the internal pop- 

 liteal. 



FLEXOR LONGUS POLLICIS. Origin, from the lower two- 

 thirds of the internal surface of the fibula, from the lower part 

 of the interosseous membrane, fascia covering tibialis posticus, 



