1. Scalp laceration belongs to specialized skin, and contains a large number of hair follicles, sweat glands and sebaceous glands, which can easily hide dirt and bacteria and easily lead to infection. However, scalp blood circulation is very rich, although scalp laceration occurs, as long as it can be thoroughly debrided in time, infection is rare. In all layers of scalp, the hat aponeurosis is a tough aponeurosis, which is not only an important structure to maintain scalp tension, but also a barrier to prevent superficial infection from invading the skull. When the scalp laceration is shallow and the cap aponeurosis is not damaged, the laceration is not easy to open, and the broken end of blood vessel is difficult to retract to stop bleeding, but there is more bleeding. If the cap aponeurosis breaks, the wound will obviously crack, and the broken end of the injured blood vessel will contract and solidify with the wound, so there is less bleeding. (1) Simple scalp laceration? Often due to sharp instrument stab or cut, the split is straight, the wound edge is neat and without defect, and the depth of the wound varies with the injury factors. Except for a few sharp instruments that directly pierce or chop into the skull and cause open craniocerebral injury, most simple lacerations are limited to the scalp, sometimes reaching the periosteum, but the skull is often intact without brain injury. (2) Complex scalp laceration? Often caused by blunt trauma or head collision with foreign bodies. Laceration is irregular, and there are contusion marks on the edge of the wound. There are still fibers connected between internal lacerations, which are not completely broken, that is, there is no "tissue collapse" phenomenon. In forensic identification, if scalp contusion's wound appears "tissue collapse", it often implies that it is caused by metal or angular weapons. The shape of the wound can often reflect the size and shape of the wound. This kind of trauma is often accompanied by skull fracture or brain injury. In severe cases, it can also cause comminuted concave fractures or perforated fractures penetrating into the skull, so foreign bodies such as hair, cloth scraps or sediment are often embedded, which is easy to cause infection. When examining the wound, be careful not to take out the foreign body embedded in the skull to avoid sudden bleeding. (3) Scalp laceration? Most of them are caused by oblique or tangential scalp violence. The torn scalp is often tongue-shaped or petal-shaped, and the head is often connected with a pedicle. Scalp laceration is generally not accompanied by skull and brain injury, but it is not necessarily. Occasionally there is skull fracture or intracranial hemorrhage. This kind of patients lost a lot of blood, but the degree of shock was mild. 2. Scalp avulsion injury Scalp avulsion injury is a serious scalp injury, which is almost always caused by women who wear braids accidentally rolling their hair into the rotating wheel. Because the epidermis layer, subcutaneous tissue layer and cap aponeurosis layer are closely connected, the scalp is often torn off from the cap aponeurosis space under strong pulling, and sometimes it is torn off with part of periosteum, leaving the skull exposed. The range of scalp avulsion is related to the area of hair root involvement. In severe cases, it can reach the full coverage area of the hat aponeurosis, from the front to the upper eyelid, nasal root, and then to the hairline, involving the auricle and even both cheeks. The patient loses a lot of blood, which can cause shock, but it is not complicated with skull fracture or brain injury. 3. Scalp hematoma The scalp is rich in blood vessels. After being hit or collided by a blunt object, the blood vessels in the tissue can rupture and bleed, but the scalp is still intact. Scalp hemorrhage often forms hematoma under subcutaneous tissue, hat aponeurosis or periosteum. Its location and type are helpful to analyze the injury mechanism and estimate the degree of craniocerebral injury. (1) Subcutaneous hematoma? The subcutaneous tissue layer of scalp is the intersection of scalp blood vessels, nerves and lymph, which is easy to bleed and edema after injury. Because the hematoma is located between the superficial layer and the cap aponeurosis, limited by the subcutaneous fibrous membrane, it has its special manifestations: small volume and high tension; The pain is very significant; When seeing a doctor, the center is slightly soft and the peripheral uplift is hard, which is often mistaken for a concave fracture. (2) Cap subdural hematoma? The lower layer of cap aponeurosis is a loose honeycomb tissue layer, between which there are blood vessels connecting scalp vein with skull plate vein and intracranial venous sinus. When the head is subjected to oblique violence, the scalp slides violently, causing the blood vessels between layers to tear, and the bleeding is easy to spread, often causing huge hematoma. Therefore, its clinical characteristics are: a wide range of hematoma. In severe cases, the hematoma boundary is consistent with the attachment edge of the hat aponeurosis, reaching the eyebrow arch in front, the occipital tuberosity and the nape line in the back, and reaching the zygomatic arch on both sides, just like a hat resting on the patient's head. Hematoma has low tension, obvious fluctuation, light pain and anemic appearance. Huge cap-shaped subdural hematoma in infants can cause shock. (3) Subperiosteal hematoma? Subperiosteal hematoma of skull is usually accompanied by linear fracture of skull, except for birth injury or fetal head suction midwifery. The main sources of bleeding are lamellar hemorrhage or periosteum peeling, and hematocele between periosteum and skull surface. Its clinical feature is that the periphery of hematoma stops at the suture. This is because the periosteum clip is embedded in the bone seam during the development of skull, and few subperiosteal hematomas exceed the bone seam. Unless the fracture line crosses two skulls, the hematoma will still stop at the suture of the other skull.