Pelvic girdle also consists of two similar halves meeting in the mid-line by a vertical ligament.
Each half is known as os-innominatum and composed of ilium, pubis, and ischium. All these three bones are not fused with each other. At their meeting points on the outer surface is a concave acetabulum for the head of humerus.
Ilium is strong, compressed, rod-like bone directed upwards and backwards to articulate with the sacral vertebrae (within the groove of transverse process of I sacral).
On the outer side it is produced into a pre-acetabular process in front of the acetabulum and also contributes in the formation of about one-third part of acetabulum.
Pubis is flat and slightly curved bone, passes downwards to meet in front with its fellow of the other side in the middle line at the pubic symphysis. Between the anterior ends of two pubes is present a backwardly directed nodule of calcified cartilage, the epipubis.
On the anterior end near its fusion with the ilium and ischium it has an oval foramen for the obturator nerve. Just external and slightly posterior to the foramen is a small rod-like process, the prepubis, which is directed outwards. Pubis also contributes to about one-third of the acetabulum.
Ischium is a flat and slightly curved bone, runs inward to meet its fellow of the other side at the ischiatic symphysis. It articulates on the outer side with the pubis and ilium of its side.
A small rhomboidal piece of calcified cartilage, hypoischium, is present in between the two ischia at the anterior face of ischiatic symphysis and gives support to the ventral wall of cloaca.
Ischium also forms about one-third of the acetabulum. The acetabulum is a cup-shaped cavity situated on the outer side at the point where all the three bones of each half of pelvic girdle join with each other. It provides articular surface for the head of femur.
A wide space is present between the pubes and ischia of both sides which is divided into two lateral ischio-pubic fenestrae by a median ligament. The ligament is often lost in the dried girdle.