GLUTEAL REGION. 337 



the lower margin of the Glutens minimus. It is situated partly within the pelvis 

 at its posterior part, and partly at the back of the hip-joint. It arises from the 

 front of the sacrum by three fleshy digitations, attached to the portions of bone 

 interposed between the second, third, and fourth anterior sacral foramina, and 

 also from the grooves leading from the foramina ; a few fibres also arise from the 

 margin of the great sacro-sciatic foramen, and from the anterior surface of the 

 great sacro-sciatic ligament. The muscle passes out of the pelvis through the 

 great sacro-sciatic foramen, the upper part of which it fills, and is inserted, by a 

 rounded tendon, into the upper border of the great trochanter, being generally 

 blended with the tendon of the Obturator internus. 



Relations. By its anterior surface, within the pelvis, with the Eectum (especially 

 on the left side), the sacral plexus of nerves, and the internal iliac vessels ; external 

 to the pelvis, with the os innominatum and capsular ligament of the hip-joint. By 

 its posterior surface, within the pelvis, with the sacrum ; and external to it, with the 

 Gluteus maximus. By its upper border, with the Gluteus medius, from which it 

 is separated by the gluteal vessels and nerves. By its lower border, with the 

 Gemellus superior ;' the ischiatic vessels and nerves, the internal pudic vessels and 

 nerve, arid the nerve to the Obturator internus, passing from the pelvis in the 

 interval between them. 



Dissection. The next muscle, as well as the origin of the Pyriformis, can only be seen when 

 the pelvis is divided, and the viscera contained in this cavity removed. 



The Obturator Internus, like the preceding muscle, is situated partly within the 

 cavity of the pelvis, partly at the back of the hip-joint. It arises from the inner 

 surface of the anterior and external wall of the pelvis, being attached to the 

 margin of bone around the inner side of the obturator foramen ; viz., from the 

 descending ramus of the pubes, and the ascending ramus of the ischium ; and 

 laterally, from the inner surface of the body of the ischium, between the margin 

 of the obturator foramen in front, the great sacro-sciatic notch behind, and the 

 brim of the true pelvis above. It also arises from the inner surface of the obturator 

 membrane and from the tendinous arch which completes the canal for the passage 

 of the obturator vessels and nerve. The fibres are directed backwards and down- 

 wards, and terminate in four or five tendinous bands, which are found on its deep 

 surface ; these bands are reflected at a right angle over the inner surface of the 

 tuberosity of the ischium, which is covered with cartilage, grooved for their 

 reception, and lined with' a synovial bursa. The muscle leaves the pelvis by the 

 lesser sacro-sciatic notch ; and the tendinous bands unite into a single flattened 

 tendon, which passes horizontally outwards, and, after receiving the attachment 

 of the Gemelli, is inserted into the upper border of the great trochanter in front 

 of the Pyriformis. A synovial bursa, narrow and elongated in form, is usually 

 found between the tendon of this muscle and the capsular ligament of the hip. 

 It occasionally communicates with that between the tendon and the tuberosity of 

 the ischium, the two forming a single sac. 



In order to display the peculiar appearances presented by the tendon of this muscle, it should 

 be divided near its insertion and reflected outwards. 



Relations. Within the pelvis, this muscle is in relation, by its anterior surface, 

 with the obturator membrane and inner surface of the anterior wall of the pelvis ; 

 by its posterior surface, with the pelvic and obturator fascias, which separate it 

 from the Levator ani ; and it is crossed by the internal pudic vessels and nerve. 

 This surface forms the outer boundary of the ischio-rectal fossa. External to the 

 pelvis, it is covered by the great sciatic nerve and Gluteus maximus, and rests 

 on the back part of the hip-joint. 



The Gemelli are two small muscular fasciculi, accessories to the tendon of the 

 Obturator internus, which is received into a groove between them. They have 

 received the names superior and inferior from the position they occupy. 



The Gemellus Superior, the smaller of the two, arises from the outer surface of 

 the spine of the ischium, and, passing horizontally outwards, becomes blended 

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