THE PELVIS. 471 



rough, triangular surface, for articulating with the pubis ; 

 and inferiorly and posteriorly, another for articulating 

 with the ischium. 



The ala is the broad portion which expands upward and 

 outward from the body; it has two surfaces and a circum- 

 ference. Its external surface is rough, and irregularly con- 

 vex and concave, and is called the dorsum. This surface 

 has two semicircular lines a superior and inferior. The 

 superior is long, usually well marked, begins a short dis- 

 tance behind the anterior superior spinous process, and 

 takes a curved direction backward to the posterior part of 

 the great sciatic notch. To this line, and all that part of 

 the dorsum above, and between it and the upper edge of 

 the ilium, with the exception of a small posterior portion, 

 the gluteus medim muscle is attached. This excepted pos- 

 terior part gives attachment to the gluteus maximus. The 

 inferior line, a short distance above the acetabulum, curves 

 backward from the anterior inferior spinous process to the 

 fore part of the sciatic notch. To this line, and to the 

 space between it and the superior line, the gluteus minimus 

 muscle is attached. Below the inferior line, the body be- 

 comes prominent, and gives attachment to a part of the 

 gluteus minimus the external tendon of the rectus/emorts 

 muscle, and a portion of the capsular ligament. 



The internal surface of the ilium, called the venter, has its 

 central and superior part very concave for lodging the 

 iliacus internus muscle ; there is also seen upon it an ob- 

 lique canal for the nutritious artery. Below the venter 

 there is a rounded edge which is continuous with one from 

 the promontory of the sacrum behind, and the pubis before, 

 called the linea-ileo pectinea. All the surface above thia 

 line enters into the false pelvis. The small surface below 

 it, and above the sciatic notch, helps to form the true 

 pelvis. 



The posterior part of this internal surface, is rough, and 

 divided into two portions : the anterior, covered with car- 

 tilage, and articulating with the sacrum; and the posterior, 

 rough for the attachment of the sacro sciatic-ligaments. 



