First, the shape of a person's skull is basically the same as the number of bone fragments. No one has a long skull on the back of his head or a different skull. The back of the head is just a conceptual thing, and there is no substantive object to speak of.
Second, seeing the cheek behind the head means that the cheekbones on both sides of the face and chin are relatively enlarged, horizontal and even the bone angle is obvious. Even if you look from the back, you can clearly see the acute angle of the cheekbone, which is called seeing the cheek behind the head, or; On the other hand, you can see bones. The derogatory term is "the back of the head looks at the back bone." There are many faces that are anti-bone, and gills are seen at the back of the head.
Third, in the Three Kingdoms period, Wei Yan was indeed occipital, but the ratio of introversion was low. Moreover, he can achieve Wei Yan's position, has become a middle-level cadre in the army, and is a valuable bone among all sentient beings.