axis (aks'is)

PL axes. i. A fixed line, actual or imaginary, about which anything revolves. 2. The central part of anything; hence a line occupying the center of anything or about which other parts are symmetrically disposed (a. of symmetry). 3. Any particular diameter of an object, especially its long diameter. 4. In optics, the name given to the lines pa ing through the optical center. 5. [B. N. A., epistrophe us.] The second cervical vertebra, so-called because. the atlas and the cranium turn upon its odontoid proce (dens) as upon a pivot, a. ' cord. See primitive streak under streak, a. -cylinder. Syn.: axial fiber, neuraxon. The central and e ential part of every nerve fiber, its size varying directly with that of the whole fiber, a. -cylinder proce . See under proce , a. fiber. See a.-cylinder. a. nbrillae. See primitive Hbrillae, under Hbrilla. a. of the cochlea. See modiolus. a. of crystallization. A line about which the particles of a crystal are more or le symmetrically disposed. [Lat., axis, axle, pivot, pole.]