PLANE

n. Plan. Lat., planum. Fr., plan. Ger., Ebene. 1. A level surface; a surface such that if any two of its points are joined by a straight line that line will lie wholly within the surface, [a. 35.] 2. An ideal plane as above defined, used as a basis or standard of reference by means of which the positions of the parts of a body or organism are indicated, [a, 48.] Alveolocondylar p. The p. tangent to the alveolar point and most prominent points on the lower aspects of the condyles of the occipital bone. [L.] Anterior focal p. See Focal p'.s. Anterior (lateral) inclined p. of the pelvis. See Inclined p's of the pelvis. Anterior principal p. See Principal p's. Coccygeal p. The fourth parallel p. of the pelvis. Diagonal p. Of a flower, any vertical p. which is not antero-posterior or lateral. [B, 279.] Double-inclined p. Two boards united by hinges and resting upon a third; used to support the lower limb flexed in the treatment of fractures. [E.] First focal p. See Focal p's. First principal p. See Principal p's. Focal p's. Two p's drawn respectively through the anterior and posterior principal foci of a dioptric system (e. g., the eye) and perpendicular to the line (axis of the system) connecting the two. The p. pa ing through the anterior focus is called the anterior (or first) focal p.; that pa ing through the posterior focus the posterior (or second) focal p. [B.] Glabello-occipital p. The vertical p. of the maximum antero-posterior diameter of the skull. [L.] Horizontal p. of van Ihering. See Van Iherinofs p. Inclined p. Ger., schiefe Ebene. A surface situated obliquely to the p. of the horizon; one of the elementary mechanical powers, [a, 48.] Inclined p's of the pelvis. " The sciatic spines," says Lusk, " divide the pelvic cavity into two unequal sections. In the larger, anterior section, the lateral walls slope toward the symphysis and arch of the pubes, while posteriorly the walls slope in the direction of the sacrum and coccyx. The declivities in front of the spines are termed the anterior inclined p's of the pelvis, over which rotation of the occiput takes place in tne mechanism of normal labor. Behind the spines the lateral slopes are known as the posterior inclined p's." [A, 22.] Medial p., Median p., Mesial p. Lat., meson. Ger., Me diane bene. A p., usually antero-posterior, which divides a body or organ into two equal and symmetrical parts. The median p. of the body is known as the meson. [L; a, 48.] Naso-iniac p. The cutting the nasion and the inion. [L.] Naso-opisthiac p.?.he p. cutting the nasion and opisthion. [L.] Orbital p. See PLANUM orbitale. Parallel p's of the pelvis. P's intersecting the axis of the pelvic canal at right angles, and therefore in reality not parallel. Four such p's are distinguished; the first parallel p. of the pelvis is the p. of the superior strait; the second is the p. extending from the middle of the sacral vertebra to the level of the subpubic ligament; the third is the p. at the level of the spines of the ischia; and the fourth is the p. at the outlet. [A, 30.] -P. of refraction. A p. pa ing through a refracted ray of light and drawn perpendicular to the surface at which refraction takes place. [B.] P. of regard. A p. pa ing through the centre of rotation of the eye and the fixation point. [Helmholtz (a, 29).] P. of the chasm a. Fr., plan du chasm a. Ger., Chasmaebene. The p. tangent to the punctum spinae nasal is posterior is and the punctum for am in is magni anterius. [Li auer (L).] P's of the pelvis. Fr., plans du ba in. Imaginary p's touching the same parts of and posterior principal points of a dioptric system (e. g., the eye) and perpendicular to the line (axis of the system) connecting the two. The p. pa ing through the anterior principal point is called the anterior (or first) principal p.; that pa ing through the second principal point tne posterior (or second) principal p. [B.] Sagittal p. The median antero-posterior p. of the body, [a, 48.] Second focal p. See Focal p's. Second principal p. See Principal p's. Single-inclined p. A support for the lower limb in the treatment of certain fractures, consisting of a board laid under the limb which is raised at the distal end and inclines downward to the buttocks. Van Ihering's p. A p. tangent to the lower margin of the orbit and pa ing through the auricular points. IL.] Visual p. Fr., plan visuel. Ger., Visirebene, Blickebene. A p. pa ing through the visual axis. [B.] A, ape; A, at; A, ah; A, all; Ch, chin; Ch, loch (Scottish); [s. 282]