Jaw (anatomy)
The jaw ( Greek Γνάθος gnathos ; Bavarian / Austrian also in standard language: the jaw) is used by most vertebrates for feeding and is therefore usually toothed. It consists of the upper jaw ( Latin maxilla ) and the lower jaw (Latin mandibula ). The teeth are anchored in the jaws in the tooth sockets (alveoli) via a gomphosis (wedge).
Mammals
In the case of mammals , the lower jaw is in the TMJ ( temporomandibular joint ) movable on the temporal bone ( temporal Os ) attached. During the embryonic development , the temporomandibular joint lies elsewhere (see below in birds), which is why it is referred to comparatively anatomically as the secondary temporomandibular joint. The upper and lower jaw are only indirectly connected to one another. The upper jaw is immobile in mammals, with them only the lower jaw is moved by the masticatory muscles . The two halves of the jaw are completely fused.
Birds
Birds' lower jaws (aves) are made up of several fused bones. One of them, the articular bone, corresponds to the articular process of the lower jaw in mammals. In birds, the opposite side of the skull is formed by the os quadratum . This cranial bone is still involved in the formation of the primary temporomandibular joint in mammals, but is then shifted into the middle ear as one of the ossicles (hammer, malleus ), so that a secondary temporomandibular joint is necessary. Another special feature of the birds is that the upper jaw (upper beak) is attached to the skull in a moveable manner by a connective tissue elastic zone and is thus actively involved in the opening of the beak. The jaws of recent birds are toothless.