The skull consists of a solid and complete neurocranium, to which many of the other bones are only loosely attached, particularly the highly mobile jaw bones, which facilitate manipulation and ingestion of large prey items. The left and right sides of the lower jaw are joined together only by a flexible ligament at the anterior tips, allowing them to separate widely, and the posterior end of the lower jaw bones articulate with a quadrate bone, allowing further mobility. The mandible and quadrate bones can pick up ground-borne vibrations; because the sides of the lower jaw can move independently of one another, a snake resting its jaw on a surface has sensitive stereo auditory perception, used for detecting the position of prey. The jaw–quadrate–stapes pathway is capable of detecting vibrations on the angstrom scale, despite the absence of an outer ear and the lack of an impedance matching mechanism—provided by the ossicles in other vertebrates—for receiving vibrations from the air.