A MANUAL OF ZOOLOGY 61 



femoris. These three heads unite near the middle of 

 the thigh into the tendon of the patella, whose insertion is 

 on the ventral proximal end of the tibio-fibula. The vastus 

 externus is the most dorsal of these three heads, with its 

 origin on the posterior surface of the ilium. The vastus 

 internus lies nearer the ventral surface, ventral to the 

 rectus anticus femoris and external to the sartorius with 

 its origin on the anterior surface of the head of the femur 

 and the acetabulum. The rectus anticus femoris is the 

 middle head with its origin on the ventral posterior border 

 of the ilium. 



The Superficial IVIuscies of the Dorsal Surface of the 

 Thigh — The gluteus is a thick muscle with its origin on 

 the outer posterior surface of the ilium, and with its 

 "insertion on the posterior surface of the cartilage about 

 the head of the femur. The largest muscle on the dorsal 

 surface is the' semimembranosus. It is bounded by the 

 vastus externus and the rectus internus minor. It origin- 

 ates on the ischium and is inserted on the knee joint in 

 its aponeurosis. The long spindle shaped muscle with 

 two bellies with a common tendon at the proximal end 

 is the biceps femoris. It is bounded by the triceps femoris 

 and the semimembranosus, and has its origin near the dorsal 

 edge of the acetabulum. A part of this muscle is inserted on 

 the dorsal proximal half of the femur and another part is in- 

 serted on the knee joint and the dorsal part of the proxi- 

 mal end of the tibio-fibula. The pyriformis is a small 

 muscle with its origin on the posterior end of the urosfyle 

 and its insertion on the shaft of the femur. 



Deen Muscles of the Dorsal Surface of the Thigh — 

 After removing the vastus externus, the semimembrano- 

 sus, and the biceps f-emorls, the ilio-psoas will be seen in 

 contact with the ventral border of the gluteus. Remove 

 the gluteus and find the origin of this muscle on the inner 

 posterior surface of the ilium internal to the acetabulum. 

 Follow it around the ventral border of the ilium, anterior 

 to the acetabulum, to its insertion on the dorsal border 

 of the femur. Ventral to the origin of the semimembrano- 

 sus and dorso-posterior to the obturator find the quadra- 

 tus femoris. It originates on the ilium near the acetabu- 

 lum and is inserted on the proximal third of the femur; 



