The two bones on the cat's back protrude and the middle is concave.

This condition is often referred to as "bony protrusion" or "saddle back". The cat's spine consists of many vertebrae, which are connected by cartilage. Sometimes, these connections may have problems, resulting in the reduction or disappearance of intervertebral cartilage in the back, which leads to the protrusion and depression of the back bones.

This situation is usually caused by malnutrition or lack of proper exercise, which means that you need to provide your cat with a better diet and more exercise. If you find that your cat has a serious depression in its back, or its athletic ability is affected, you should take it to the vet.

Veterinarians may recommend an X-ray examination to determine whether there are bone and soft tissue problems. If the examination results show that there is something wrong, the doctor may suggest physical therapy and exercise to strengthen back muscles and improve bone health.

In short, the cat's back depression is not a normal phenomenon and needs to be paid attention to. Provide proper diet and exercise, check your cat's health regularly, and ask the veterinarian to check any abnormal symptoms to ensure that your cat stays healthy and happy.