SACRO-SCTATIC LIGAMENTS. 



545 



the bones after the other ligaments are examined, the cartilage may be 

 detached with a knife. 



Movement. There is scarcely any appreciable motion in the sacro-iliac 

 articulation, even when the hip-bone is seized by the hand, and forcibly 

 pulled in different directions. The articulation seems designed for se- 

 curity and little movement, inasmuch as the surfaces are not in contact, 

 are very irregular, and have a firm and inextensible piece of cartilage 

 interposed between them. In some instances, and especially during preg- 

 nancy, there is a greater degree of motion perceptible. 



Two sacro-sciatic ligaments pass from the lateral part of the sacrum 

 and coccyx to the hinder border of the os innominatum, across the space 

 between the bones at the back of the pelvis : they are named large and 

 small. 



The large ligament (fig. 190, a) reaches from the back of the hip bone, 

 and the side of the sacrum and coccyx to the ischial tuberosity. As this 



Fig. 189. 



Fie. 190. 



This figure shows the irregular piece of carti- 

 lage (a) in the sacro-iliac articulation. 



SACRO-SCIATIC LIGAMENTS. 



a. Large or posterior ligament. 



b. Small or anterior ligament. 



may have been cut in the examination of the gluteal region, no further 

 notice is given here ; but if it remains entire, see Dissection of the But- 

 tock for its description. 



The small ligament (fig. 190, b) is attached internally by a wide piece 

 to the border of the sacrum and coccyx, where it is united with the origin 

 of the preceding band. The fibres are directed outwards, and are inserted 

 by a narrowed part into the ischial spine of the hip bone. Its pelvic sur- 

 face is covered by the coccygeus muscle ; and by the opposite surface it 

 is in contact with the great sacro-sciatic ligament. Above it is the large 

 sacro-sciatic foramen ; and below it is the small foramen of the same name, 

 which is bounded by the two ligaments. 



By their position these ligaments convert into two foramina (sacro- 

 sciatic), the large sacro-sciatic excavation in the dried bones : the open- 

 ings, and the parts they give passage to, are described with the Buttock. 

 35 



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