The bone is located above the spine and consists of 23 flat bones and irregular bones of different shapes and sizes (3 pairs of ossicles in the middle ear are not included). Except the mandible and hyoid, the other bones are firmly connected with each other by suture or cartilage, which plays the role of protecting and supporting the brain, sensory organs, digestive tract and the initial part of respirator. The cranium is divided into two parts: cranium and facial cranium. The cranium is located in the posterior upper part of the skull. There is a cranial cavity in it, which contains 8 pieces of brain. The facial cranium is the anterior and inferior part of the skull, including the orbit, nasal cavity, oral cavity and other structures, forming the facial stent, a total of 15 pieces.