XIV THE MUSCULAR SYSTEM 251 



action of the muscle under these different conditions depends 

 upon the change in the fulcrum which is brought about by 

 the bending of the leg. 



The grac ilis minor is a slender muscle which arises from 

 a tendon behind the ischiac symphysis. Distally it joins the 

 tendon of insertion of the gracil is major. The muscle is 

 also attached to the skin of the posterior side of the thigh. 

 Its action is similar to that of the gracilis major. 



The two following muscles appear on the dorsal side of 

 the thigh : the semimembranosus, a large muscle lying on 

 the posterior side of the dorsal surface of the thigh just 

 above the gracilis major. It arises by a broad fleshy attach- 

 ment from the dorsal half of the posterior margin of the 

 ischium. It is inserted by a short tendon which passes 

 beneath the tendon of origin of the gastrocnemius into the 

 proximal end of the tibio-fibula behind the knee. There is 

 an oblique tendinous inscription running across this muscle 

 as in the gracilis major. The semimembranosus adducts the 

 thigh, or pulls it backward, and, like the gracilis, flexes or 

 extends the leg according to whether it is in a flexed or an 

 extended position. 



The ileo-jibularis, a slender muscle lying between the 

 semimembranosus and the posterior head of the triceps 

 femoris. It arises from the ileum, just behind the posterior 

 end of the dorsal crest, and it is inserted into the proximal 

 end of the fibula. It draws the thigh dorsally and flexes the 

 leg. s 



The semitendinosiis, a slender muscle which is covered by 

 the gracilis major. It arises by two tendinous heads from 

 the ischium. The ventral head passes between the dorsal 

 and ventral heads of the adductor magnus and affords a 

 point of attachment for the small third head of the latter 

 muscle. The two heads unite near the middle of the 



