External Surface
The external surface, known as the dorsum ilii, is directed backward and lateralward behind, and downward and lateralward in front.
It is smooth, convex in front, deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders.
This surface is crossed in an arched direction by three lines—the posterior, anterior, and inferior gluteal lines.
The posterior gluteal line (superior curved line), the shortest of the three, begins at the crest, about 5 cm. in front of its posterior extremity; it is at first distinctly marked, but as it passes downward to the upper part of the greater sciatic notch, where it ends, it becomes less distinct, and is often altogether lost.
Behind this line is a narrow semilunar surface, the upper part of which is rough and gives origin to a portion of the Glutæus maximus; the lower part is smooth and has no muscular fibers attached to it.
The anterior gluteal line (middle curved line), the longest of the three, begins at the crest, about 4 cm. behind its anterior extremity, and, taking a curved direction downward and backward, ends at the upper part of the greater sciatic notch.
The space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Glutæus medius.
Near the middle of this line a nutrient foramen is often seen.
The inferior gluteal line (inferior curved line), the least distinct of the three, begins in front at the notch on the anterior border, and, curving backward and downward, ends near the middle of the greater sciatic notch.
The surface of bone included between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutæus minimus.
Between the inferior gluteal line and the upper part of the acetabulum is a rough, shallow groove, from which the reflected tendon of the Rectus femoris arises.
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