THE MUSCLES OF THE HIND-LIMB. 69 
d. Deep muscles of the thigh. 
Lay the frog on its back so as to dissect the thigh from the 
preaxial surface. Separate the adductor magnus and rectus 
internus major with blunt instruments so as to expose :-— 
i. The semitendinosus: 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 magnus and 
} unites with the posterior head in the distal third 
. of the thigh. The tendon of insertion 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 ends backwards and forwards, so as to expose 
ii, The adductor brevis: 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. 
iil, The pectineus : 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 brevis, 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 
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 : a small muscle on the back 
of the upper part of the thigh; it arises from the 
ilium above the acetabulum, and from the base 
