The oblique projection of the lumber spine is used to demonstrate the.. Transverse processes

 The oblique projection of the lumber spine is used to demonstrate the:

• a- spinous processes
• b- Transverse processes
• c- Apophyseal joint
• d- Upper sacrum

While all the listed structures can be seen on an oblique projection of the lumbar spine, the primary purpose of this specific view is to visualize: c. Apophyseal joints

Here's why:

a. Spinous processes:

These are visible in both AP and lateral projections, so wouldn't require the extra oblique view.

b. Transverse processes:

While partially visible, they are obscured by the vertebral bodies in the oblique view. Other projections like lumbar flexion or extension show them better.

d. Upper sacrum:

The upper sacrum may be seen but it's not the main focus of the oblique view.

c. Apophyseal joints:

These, also known as facet joints, are best visualized on an oblique projection as they are angled and partially hidden in the AP view. The oblique angle allows for clear visualization of the joint surfaces and alignment, which is crucial for diagnosing certain spinal conditions like spondylolisthesis or facet joint arthritis.

Therefore, while other structures are visible, the primary purpose of the oblique projection of the lumbar spine is to assess the apophyseal joints.