COMPARATIVE ANATOMY 41 



of Achilles, which should be carefully split open to demonstrate 

 this fact. The tendon of the plantaris passes through a groove 

 and inserts on the ventral side of the calcaneus. 

 Action: to extend the foot. 



26. SoLEUS. — This is the remaining muscle of the calf of the 

 leg with an insertion on the tendon of Achilles. It lies on the 

 lateral side and originates from the proximal half of the 

 fibula. 



Action: to extend the foot. 



27. Flexor Digitorum Brevis. — This is a flat muscle on the 

 sole of the foot. It originates from the tendon of the plantaris, 

 a fact revealed by removal of the plantaris tendon at its insertion 

 on the calcaneus. Distally the flexor digitorum brevis divides 

 into four tendons, one going to each toe. 



Action: to flex the toes. 



28. QuADRATUS Plantae. — Cut through the middle of the 

 flexor digitorum brevis and expose the wide tendon beneath. 

 This is the combined tendon of the flexor digitorum longus and 

 the flexor hallucis longus. On it is inserted the small triangular 

 quadratus plantae muscle, which originates from the lateral 

 surface of the calcaneus and cuboid. 



Action: to hold the tendon in place. 



29. Flexor Digitorum Longus. — Beginning on the sole 

 of the foot trace back the smaller and more medial branch of the 

 combined tendons of the flexor digitorum longus and the flexor 

 hallucis longus until this muscle is reached. The flexor digi- 

 torlum longus originates from the surface of the tibia and the 

 head of the fibula. Distally the tendon, after the flexor hallucis 

 longus has united with it, divides into four branches, one for 

 each toe. 



Action: to flex the toes and extend the foot. 



30. Flexor Hallucis Longus. — This muscle lies lateral to 

 the flexor digitorum longus and greatly exceeds it in size. It 

 originates from the shaft of the tibia, and from the head and 

 shaft of the fibula. In five-toed mammals the tendon of the 

 flexor hallucis longus inserts on the big toe (hallux); in the cat 

 it unites with the tendon of the flexor digitorum longus. 



Action: with the flexor digitorum longus to flex the toes and 

 extend the foot. 



