230 



THE SKELETON. 



broad shallow groove over which passes the Iliacus muscle. The posterior 

 border of the ilium, shorter than the anterior, also presents two projections sepa- 

 rated "by a notch, the posterior superior and the posterior inferior spinous pro- 

 cesses. The former corresponds with that portion of the posterior surface of 



Pig. 165. Right Qs Innominatum. Internal Surface. 



the ilium which serves for the attachment of the sacro-iliac ligaments ; the latter 

 to the auricular portion which articulates with the sacrum. Below the poste- 

 rior inferior spinous process is a deep notch, the great sacro-sciatic. 



The Ischium forms the lower and back part of the os innominatum. It is 

 divisible into a thick and solid portion, the body ; the tuberosity, a large rough 

 eminence, on which the body rests in sitting ; and a thin ascending part, the 

 ramus. 



The body, somewhat triangular in form, presents three surfaces, external, in- 

 ternal, and posterior. The external surface corresponds to that portion of the 

 acetabulum formed by the ischium ; it is smooth and concave above, and forms 

 a little more than two-fifths of that cavity ; its outer margin is bounded by a 



