MUSCLES OF THE HIND-LIMB. 75 



d. Deep muscles of the thigh. 



Lay the frog on its hack and dissect the thigh from the 

 preaxial surface. Seijarate the adductor magnus and the rectus 

 internus major with hlimt instruments so as to expose the follow- 

 ing muscles : 



i. The semitendinosus is a long thin muscle which 

 arises by two heads; an anterior one from the 

 ischium close to the ventral angle of the ischial 

 symphysis and the acetabulum ; and a posterior 

 one from the ischial symphysis. The anterior 

 head passes through a slit in the adductor mag- 

 nus and unites with the posterior head in the 

 distal third of the thigh. The tendon of inser- 

 tion is long and thin, and joins that of the rectus 

 internus minor to be inserted into the tibia just 

 below its head. 



Divide the adductor magnus and the sartorius in the middle 

 and turn the cut eyids backwards and forwards, so as to expose the 

 following muscles: 



ii. The adductor hrevis is a short wide muscle, lying 

 beneath the upper end of the adductor magnus. 

 It arises from the pubic and ischial symphyses, 

 and is inserted into the preaxial surface of the 

 proximal half of the femur. 



iii. The pectineus is a rather smaller muscle, lying along 

 the outer (extensor) side of the adductor brevis. 

 It arises from the anterior half of the pubic sym- 

 physis in front of the adductor hrevis, and is 

 inserted like it into the proximal half of the femur. 



iv. The ilio-psoas arises by a wide origin from the 

 inner surface of the acetabular portion of the 

 ilium : it turns round the anterior border of the 

 ilium, and crosses in front of the hip joint, where 

 for a short part of its course it is superficial 

 between the heads of the vastus internus and of 

 the rectus anticus femoris : it then passes down 

 the thigh beneath these muscles, and is inserted 

 into the back of the proximal half of the femur. 



V. The quadratus femoris is a small muscle on the back 

 of the upper part of the thigh : it arises from the . 



