MUSCLES OF THE THIGH. 449 



It forms a conical belly, which passes out of the pelvis at the 

 upper part of the sacro-sciatic foramen, receiving a slip of fibres 

 from the posterior inferior spinous process of the ilium. 



It is inserted, by a round tendon, into the upper middle part 

 of the trochnnter major within the insertion of the glutaeus me- 

 dius. 



It rotates the limb outwards. Between its tendon and the su- 

 perior geminus a small bursa exists.* 



The Gemini, 



Are two small muscles, closely connected with each other, 

 which are situated lower down on the pelvis than the pyrifor- 

 mis. The upper one arises from the posterior part of the root , 

 of the spinous process of the ischium ; the lower from the upper 

 back part of the tuberosity of the ischium. 



Being parallel to each other, and connected by their conti- 

 guous edges, they are inserted together into the posterior part 

 of the thigh bone at the root of the trochanter major, where the 

 deep pit is. 



They also rotate the limb outwards.f 



The Obturator Inlernus, 



Is principally situated within the cavity of the pelvis. It 

 arises, fleshy, from all the margin of the foramen thyroideum, 

 except where the obturator vessels go out; from the posterior 

 face of the ligamentous membrane stretched across it ; also from 

 the upper part of the plane of the ischium just below the linea 

 innominata; its fibres converge, and forming a tendon, pass out 

 of the pelvis over the trochlea of the ischium, between the sa- 

 cro-sciatic ligaments. 



The tendon is placed between the gemini muscles, which 

 form a sheath for it; and it is inserted into the pit on the back 

 of the os femoris, at the root of the trochanter major. 



* Varieties. It is sometimes split by the sciatic nerve, and when the latter di- 

 vides very high up, by one of its portions only. 



j- Varieties. The upper one, occasionally, does not exist, whereby a striking 

 resemblance with apes is established. Sometimes both are wanting. 



38* 



