Os coxae

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Description:

The os coxae is formed from three separate bony elements that fuse during development. These elements are the ilium, ischium, and pubis. In more primitive vertebrates these three elements are distinguished as three distinct bones, however, through phylogenetic history they fuse to form the single os coxae. The junction of the three bones occurs in the hip socket, the acetabulum. The paired os coxae, with the sacrum, form the pelvic skeleton, uniting the posterior limbs to the axial skeleton. In general, the os coxae is composed of two plates of compact bone with an internal core of spongy bone. In some thin areas of the bone, the inner spongy bone is absent and there exists only a thin plate of compact bone. In other areas where the bone is thick, dense compact buttresses arise for additional strength.