. Human physiology. bone in the face, and in it is fixed the lower set of teeth. Itis the only movable bone of the skull. It gives off two processes which formjoints with sockets in the temporal bones ; and these joints are so constructed THE SKELETON 23 that the lower jaw has not only a vertical movement, but is capable also olmotion sideways and backwards and forwards. It will be observed that several bones enter into the formation of the orbitsor sockets of the eyes. The upper part of each orbit is formed by the frontaland sphenoid bones ; the inner portion by the lachrymal plate ; the lowe
. Human physiology. bone in the face, and in it is fixed the lower set of teeth. Itis the only movable bone of the skull. It gives off two processes which formjoints with sockets in the temporal bones ; and these joints are so constructed THE SKELETON 23 that the lower jaw has not only a vertical movement, but is capable also olmotion sideways and backwards and forwards. It will be observed that several bones enter into the formation of the orbitsor sockets of the eyes. The upper part of each orbit is formed by the frontaland sphenoid bones ; the inner portion by the lachrymal plate ; the lowerportion by the superior maxillary ; and the outer portion by the malar orcheek-bone. These orbits (Lat. orbita, a track in which a body turns) con-tain the eyeballs, the muscles which turn the eyeball, and a certain amount offatty matter which acts as a padding to protect the delicate organ of vision. We must now notice how the head turns on the vertebralcolumn. It has already been seen that the skull rocks or nods. Fig. 23.—The Atlas,»or First CervicalVertebra; viewed from above. i, the anterior arch; 2, the posterior arch ;3, spinal cavity ; 4, lateral processes ; 5 marksthe position of the odontoid peg of the axis :6, concave surfaces which articulate with theoccipital bone. The dotted line marks theposition of the ligament which secures thepeg. The body is absent, but is representedby the odontoid peg of the axis.
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