Acetabulum lies in pelvic girdle/pectoral girdle.

Explanation

To determine whether the acetabulum lies in the pelvic girdle or the pectoral girdle, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Acetabulum**:
- The acetabulum is a concave surface that forms part of the pelvis. It is crucial for the formation of the hip joint.

2. **Identify the Location of Acetabulum**:
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