SHOUT EOTATORS OP THE THIGH. 231 



border the obturator vessels and nei-ve pass tln-ougli the obturator foramen. The 

 extra-pelvic ijortioii lies between the gemelli and in contact with the ischium 

 and capsule of the hip joint. It is covered by the great sacro-sciatic ligament, 

 the sciatic vessels and nerves, and by the gluteus maximus. 



The gemelli (gemini) are two small narrow muscles, consisting 

 chiefly of fleshy fibres extended horizontally at each side of the tendon 

 of the obturator internus ; and they are named from their position 

 above and below the tendon. The gemellus siqjerior, which is usually 

 the smaller muscle, arises from the ischial spine ; the r/emellus inferior 

 takes origin from the upper and back part of the tuberosity of the 

 ischium. Passing outwards, they join the tendon of the internal 

 obturator muscle, covering and concealing it more or less, and along 

 with it are inserted into the digital fossa of the trochanter. Some of 

 their fibres, especially from the superior gemellus, run obliquely into 

 the tendon of the obturator. 



liclatmis. — The superior gemellus is placed immediately below the pyi'iformis ; 

 the inferior gemellus is above the quadratus f emoris, and at its insertion is close 

 to the tendon of the obturator extemus muscle. These muscles may be regarded 

 as portions of the obtm-ator internus arising externally to the pelvis. 



Varieties. — The gemellus superior is often very small, and in some cases is 

 altogether absent. The gemellus inferior has also been found absent, but more 

 rarely than the upper muscle. 



The quadratus femoris muscle, of an oblong shape, arises fi'om the 

 external border of the taber ischii, and, proceeding horizontally outwards, 

 is inserted into the greater part of the Unea qiiadrati on the posterior 

 surface of the great trochanter of the femur. 



Relations. — Superiorly this muscle is close to the inferior gemellus. Its inferior 

 border is in contact, at its origin, with the descending fibres of the adductor 

 magnus, and at its msertion with the superior or horizontal fibres. It conceals 

 the outer part of the obturator externus, and also the lesser trochanter, which is 

 separated from it by a small bursa. 



Varieties. — It may be enth-ely absent and replaced by an enlarged gemellus 

 inferior. 



The obturator externus muscle arises from the outer surface of 

 the anterior two-thirds of the obturator membrane, from the outer 

 surface of the body of the pubis, and from the rami of the pubis and 

 ischium ; its fibres extend horizontally outwards and backwards, con- 

 verging to a tendon which is directed along the groove between the 

 acetabulum and the tuberosity of the ischium, m contact at the same 

 time with the under and hinder surfaces of the neck of the femur to be 

 inserted into the trochanteric fossa below the obturator internus and 

 gemelli. 



Relations. — The deep surface of the muscle is in contact with the obturator 

 membrane, while the obturator vesseLs and nerves pass over its uj^per border. Its 

 anterior sm-f ace is covered by the upper borders of the pectineus, adductor brevis, 

 and adductor magnus ; in the gi'oove beneath the acetabulum it is in contact 

 with the lower and posterior parts of the capsule of the femiu', and close to its 

 insertion it is concealed by the quadi'atus femoris. 



Nerves. — The gluteus maximus is mainly supplied by the smaU sciatic nei"ve, 

 but also receives at its upper part a separate branch from the sacral plexus. The 

 gluteus medius and minimus are supplied by the gluteal nei've. The ijyi'ifonnis, 

 gemelli, obturator internus, and quadi'atus femoris receive special branches from 

 the sacral plexus. The obtui'ator externus is supplied by the obtui'ator nerve.. 



