GLUTEAL REGION. 415 



cially 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 superior gluteal nerve. 

 By its lower border, with the Gemellus Supe'rior and Coccygeus; the sciatic 

 vessels and nerves, the internal pudic vessels and nerve, and the nerve to the 

 Obturator Interims, passing from the pelvis in the interval between the two 

 muscles. 



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

 the pelvis is divided, and the viscera removed. ' 



The Obturator Membrane is a dense layer of interlacing fibres, which completely 

 closes the obturator foramen, except at its upper and outer part, where a small 

 oval canal is left for the obturator vessels and nerve. Each obturator muscle 

 is connected with this membrane. 



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, around the inner 

 side of the obturator foramen, being attached to the descending ramus of the 

 pubes, and the ascending ramus of the ischium, and at the side to 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 obtu- 

 rator vessels and nerve. The fibres are directed backwards and downwards, 

 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 grooved for their reception : the groove is 

 covered with cartilage, 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 receiv- 

 ing 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 must 

 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 fasciae, which sepa- 

 rate 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. Ex- 

 ternal 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 are 

 called superior and inferior. 



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 

 with the upper part of the tendon of the Obturator Internus, and is inserted 

 with it into the upper border of the great trochanter. This muscle is sometimes 

 wanting. 



Relations. By its superficial surface, with the Gluteus Maximus and the sciatic 

 vessels and nerves. By its deep surface, with the capsule of the hip-joint. By 



