sphen61d

& s. [Gr. sphèn =a wedge, and eidos=form, appearance.] A. As adj.: Resembling a wedge; wedge-shaped. B. As substantive: 1. Anat .: The sphenoid-bone (q. v.). IMG:content-0025.png:[blocks in formation] 1. Astron .: A term formerly applied to any one of the concentric and eccentric revolving transparent shells in which the heavenly bodies were supposed to be fixed, and by which they were carried so as to produce their apparent motions. The word now signifies the vault of heaven, which to the eye seems the concave side of a hollow sphere, and on which the imaginary circles marking the positions of the equator, the ecliptic, ., are supposed to be drawn. It is that portion of limitle space which the eye is powerful enough to penetrate, and appears a hollow sphere because the capacity of the eye for distant vision is equal in every direction. 2. Geom.: A solid or volume bounded by a surface, every point of which is equally distant from a sphenoid-bone, s. Anat.: A wedge-shaped bone placed acro the base of the skull near the middle, and helping to form the cavity of the cranium, the orbits, and the posterior nares. It has a central part or body, two pairs of lateral expansions called the great and small wings, and another pair pointing downward called the pterygoid proce es. (Quain.) that may be generated by revolving a semicircle about its diameter as an axis. The distance from any part of the surface_to the center is called a radius of the sphere. Every section of a sphere made by a plane is a circle, and all sections made by planes equally distant from the center are equal. A circle of the sphere whose plane pa es through the center is a great circle; all other cir cles are small circles. All great circles are equal, and their radii is equal to the radii of the sphere. (q. v.); as, the sphenoidal fi ure, the sphenoidul a scale.]