The back of the head sinks in.

If there is no strong impact, it should be a normal phenomenon: from birth to about 20 years old, the head circumference, intelligence and brain volume all increase with age, because the cranial suture has not healed during this period. By the age of 20, the cranial suture began to heal, and the head circumference and brain volume did not increase. Due to the healing of cranial suture, a small depression will be formed near the middle of the back of the head. It's normal,