pyramid (pir'am-id). i

A solid resting on a plane base of three or more sides, and having as its sides triangular planes which meet at the apex. 2. A part of the body shaped more or le like a p. 3. A large compact bundle of medullated nerve fibers situated ventrad in the medulla oblong at a, being the downward continuation of the motorial tract, anterior p's of the medulla oblong at a. A pair of oblong bodies on the anterior surface of the medulla oblong at a, separated by the anterior median fi ure, posterior p. of the medulla oblong at a. The expanded portion of the funiculus gracilis at the lower angle of the fourth ventricle, p's of Malpighii. Syn.: cones of Malpighii, coni bullosi. The pyramidal ma es of the renal cortex, composed of glomeruli, blood ve els, and convoluted tubules, situated between the medullary radii. They have the base of the p. next the surface of the kidney, and the apex terminating as a renal papilla, p. of the cerebellum, p. of the inferior vermiform proce . A small elevation near the middle of the inferior vermiform proce , between the biventral lobes. pyramid of the spinal cord. See pyramidal tract, under tract. p. of the thyroid gland. A slender conical proce of the gland which extends from the upper part of the isthmus or the adjacent part of the lobes to the hyoid bone, to which it is attached by loose fibrous ti ue, p. of the tympanum. A small, hollow bony projection on the inner wall of the tympanum, behind the oval fenestra. The stapedius muscle pa es through a small opening at its apex. [Gr., pyramis, or pyramid a, of Egyptian origin.]