Figure 1
 
 

 The pelvis is composed of 6 bones fused together, 3 on each half. This is the view from the uterine side.

Pelvic Bone Structure

Tuber Coxae - hip bones
 
Ilium - longest of the 3 bones that form the pelvis. Pelvic length correlates well with kidding ease.
 
Ischium - rear part of the pelvic structure and second largest pelvic bone. The tuber ischii (pin bone) is the most caudal part. One pin bone is located on either side of the vulva. Width between the pins does not correlate with kidding ease, as these bones are immobile.  

Other Pelvic Structures

Iliac crest  - highest part of the spine between the hips.

Sacroiliac Joint - slightly below the wings of the hip, it joins the spine and pelvic bones with cartilage, synovia and ligaments.
 
Hip Joint ( acetabulum, thurl coxofemoral joint). The ball and socket joint connects the pelvis to the femur (thigh).
 
Obturator Foramen - open space between the pubic bone and the ischium. The obturator nerve passes along the ischium and through this space to the legs.
 
Pubic Symphysis - fibrocartilaginous joint that attaches both halves of the pelvis. At maturity this joint becomes inflexible, although it remains flexible in humans and wethers.