The temporal bone is located at the base and sides of the skull and directly underneath the temple. It consists of four pieces: the tympanic part, petrous portion, mastoid portion, and the squama temporalis. The squama temporalis is so thin that it is translucent. Scaly in appearance, the temporalis muscles attach to this area. The mastoid portion is heavier and rough. It attaches to the auricular muscles of the outer ear. Foramina, or holes, exist throughout this bone to allow nerves, arteries, and veins to pass through the skull. The tympanic part is separate from the rest of the temporal pieces at birth but fuses together with the rest of the temporal bones in most mammals. Scientists believe that the tympanic part is evolutionarily linked to the angular bone found in the lower jaw of reptiles. The petrous portion, also known as petrosal ridge, is the hardest piece of the temporal bone and protects the inner ear from damage. It fuses together with the inner pieces of the mastoid and squama temporalis portions.