426 



DISSECTION OF THE PELVIS. 



Define the 

 muscles 



and the 

 levator ani. 



Pyriformis 



origin in 

 the pelvis ; 



insertion ; 



relations 

 with parts 

 around ; 



use as an 

 external 

 rotator of 

 hip-joint. 



Obturator 

 internus 



is bent over 

 ischium ; 



origin in 

 the pelvis ; 



arching of 

 its tendons 

 over the 

 hip-bone ; 



insertion ; 



relations of 

 part in 

 pelvic 

 cavity ; 



Coccygeus 

 muscle. 



Dissection. Take away any fascia or areolar tissue which may 

 remain on the muscles ; and define their exit from the pelvis, the 

 pyriformis passing through the great, and the obturator through the 

 small sacro-sciatic foramen. On the right side the dissector may 

 look to the attachment of the levator ani muscle to the pubic part 

 of the hip-bone. 



The PYRIFORMIS MUSCLE is directed outwards through the great 

 sacro-sciatic foramen to the great trochanter of the femur. The 

 muscle has received its name from its form. 



In the pelvis the pyriformis arises by three slips from the second, 

 third, and fourth pieces of the sacrum, between and external to the 

 anterior sacral foramina ; as it passes from the pelvis, it takes origin 

 also from the surface of the hip-bone forming the upper boundary 

 of the large sciatic notch, and from the great sacro-sciatic ligament. 

 From this origin the fibres converge to the tendon of insertion into 

 the great trochanter of the femur. 



The anterior surface is in contact with the sacral plexus, with the 

 sciatic and pudic branches of the internal iliac vessels, and with 

 the rectum on the left side. The opposite surface rests on the 

 sacrum, and is covered by the great gluteal muscle outside the 

 pelvis. The upper border is near the hip-bone, the gluteal vessels 

 and the superior gluteal nerve being between ; and the lower border 

 is contiguous to the coccygeus muscle, the sciatic and pudic vessels 

 and nerves intervening. 



Action. The pyriformis belongs to the group of external rotators 

 of the hip-joint ; and its use has been given with the description of 

 the rest of the muscle in the dissection of the buttock (p. 117). 



The OBTURATOR INTERNUS MUSCLE has its origin in the pelvis, and 

 insertion at the great trochanter of the femur, like the preceding ; 

 but the part outside forms an acute angle with that inside the pelvis. 



The muscle arises by a broad fleshy attachment from the obturator 

 membrane, except from a small part below, from the pelvic fascia 

 covering its surface, slightly from the bone anterior to the thyroid 

 hole and from all the smooth inclined surface of the pelvis (fig. 139, 

 p. 369) behind and above that aperture except opposite the small 

 sacro-sciatic foramen where a thin layer of fat separates the fleshy 

 fibres from the bone. The fibres are directed backwards and down- 

 wards, and end in four or five tendinous pieces, which turn over 

 the edge of the hip-bone corresponding with the small sciatic notch. 

 Outside the pelvis the tendons blend into one, which receives the 

 fibres of the gemelli and is inserted into the upper border of the 

 great trochanter of the femur. 



The muscle is in contact by one surface with the wall of the 

 pelvis and the obturator membrane ; by the other surface with the 

 obturator part of the pelvic fascia, and towards its lower border 

 with the pudic vessels and nerve. 



Action. The muscle is chiefly an external rotator of the femur 

 (p. 123). 



COCCYGEUS MUSCLE. The position and the relations of this muscle 

 may now be studied from within : it is described on p. 381. 



