a. and sb. Also 8 sphænoid, 9 sphenoïd. [ad. mod.L. sphēnoidēs, sphēnoeidēs († sphæno-), a. Gr. σφηνοειδής, f. σφήν wedge: see -OID. So F. sphénoïde (1611).]
A. adj. Sphenoid bone, a bone of irregular form situated at the base of the skull, where it is wedged in between the other bones of the cranium.
1732. Monro, Anat. (ed. 2), 76. I have seen separate … Bones at the Conjunction … of the sphenoid and parietal Bones.
1766. Phil. Trans., LVII. 119. Portions of medullary substance lying upon the sphænoid bone.
1831. R. Knox, Cloquet’s Anat., 41. The sphenoid bone is articulated with the frontal, ethmoid, occipital, parietal, and temporal bones.
1884. M. Mackenzie, Dis. Throat & Nose, II. 232. The posterior third of the roof … is formed by the body of the sphenoid bone.
B. sb. 1. Anat. The sphenoid bone; one or other of the separate parts of this.
1828. Stark, Elem. Nat. Hist., I. 28. In the fœtus the occiput is divided into four parts, the body of the sphenoid into two.
1841. T. R. Jones, Anim. Kingd., 638. These two halves may therefore be called, respectively, the anterior and posterior sphenoids.
1896. trans. Boas’ Text Bk. Zool., 362. In the basal and lateral regions in front of the parts just mentioned are the sphenoids (ali-, orbito-, and basi-sphenoid).
2. Cryst. A wedge-shaped crystal bounded by four equal and similar triangular faces.
1855. Orr’s Circ. Sci., Inorg. Nature, 435. The Rhombic Sphenoid, or, Irregular Tetrahedron, is a hemihedral form, derived from the double four-faced rhombic pyramid. Ibid. A sphenoid may be derived from every one of the pyramids previously described.
1878. Gurney, Crystallogr., 78. A closed figure bounded by four similar isosceles triangles … is sometimes called a sphenoid.
