Os. The bone of the forehead; coro-nale os, inverecundum, motopon . The external surface of this bone is smooth at its upper convex part, but below several cavities and processes are observed. At each angle of the orbit the bone juts out to form two internal and two external processes. The ridge which makes the supercilium is called the superciliary process. The lower part of the forehead, where the hair of the eye brows grows, is called ophrus. The nasal process is situated between the two internal angular processes; and the two orbitar processes are continuations of the superciliary: between these is an aperture for the reception of the ethmoid bone. At the internal angular process is a cavity for the caruncula lachrymalis; at the external angular process is another for the pulley of the musculus obliquus major. The foramina are three on each side; one in each superciliary ridge, through which a nerve, vein, and artery pass to the integuments of the forehead. Near the middle of the internal side of the orbit, in the transverse suture, or near it, is a small hole, called the internal orbitar: the orbitar interims posterior is smaller, and lies about an inch deeper in the orbit. On the inside of the os frontis there is a ridge, which, on the upper part, is imperceptible, and grows more prominent at the bottom, where there is a foramen caecum; to this ridge the falx is attached. The frontal sinus is placed over the orbits, and is divided by the septum just described. This bone is of mean thickness, between that of the os occipitis and of the parietal bones; but at theorbitar process, from the pressure of the brain and the globe of the eye, ft is almost transparent . It will be obvious that the trepan cannot be applied over the sinuses to reach the brain.