Morphology of the Primary Jaw Joint in Mammals and Reptiles/Birds (IMAGE)
Caption
(Left) Generalized schematic showing the relative position of the first pharyngeal pouch and elements in the first pharyngeal arch. The upper (green) and lower (blue) elements in the first pharyngeal arch form the primary jaw joint (red circle). (Top) Reptiles/birds. The schematic on the left shows the eardrum forming between the first pharyngeal pouch and the ear canal. It is connected to one middle ear bone and the quadrate bone (green), which is part of the upper jaw. The schematic on the right shows these bones in a lizard with the primary jaw joint located between the upper and lower jaws. (Bottom) Mammals. The schematic on the left shows the eardrum forming between the first pharyngeal pouch and the ear canal. It is connected to the hammer bone (blue), which along with the anvil (green) make up two of the three middle ear bones. The schematic on the right shows the middle ear in a human embryo, with the primary jaw joint located within the middle ear, and the hammer (blue) connected to the lower jaw.
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RIKEN
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