orbit (orbit)

[F. orbite = Sp. órbita (an at.) =Pg. It. orbita, 2. A small orb, globe, or ball. Attend, and you discern it [ambition] in the fair; Conduct a finger, or reclaim a hair, Or roll the lucid orbit of an eye. Young , Satires, v. S though communicating with the cranial cavity and the nasal and temporal fo æ, and opening forward upon the face, with the apex at the optic foramen where the optic nerve enters. Seven bones enter into the formation of each orbit, the frontal, sphenoid, ethmoid, maxillary, p palatal, lacrymal, and malar, of which the first named three are common to both orbits. Each orbit communicates with surrounding cavities by several openings, the principal of which are-with the cranial cavity by the optic foramen and sphenoidal fi ure; with the nasal fo æ by the lacrymal canal; with the temporal and zygomatic fo æ by the sphenomaxillary fi ure; with ethmoidal parts by the anterior and posterior ethmoidal fo ramina; and with the face by supra-orbital, infra-orbital, extra-orbital, and malar foramina. The orbit contains the eye and its a ociate muscular, vascu 2f 2 max ma 3 тх 0 1 me Right Orbit of Man: A, its situation in and relations to the skull; B, larger view of bones entering into its composition. a, ali sphenoid; f. frontal; lacrymal; le, os planum of ethmoid; m, malar; ma, toid proce ; me, mes ethmoid, di viding the nasal fo a; mx, maxillary; n, nasal bones; o, or bito sphenoid, parietal phenom sphenoidal fi ure; 3, infra-orbital foramen. lar, glandular, sustentacular, mucous, and nervous struc tures. 4. In ornith., the orbita, or cir cum orbital region of a bird's head; the skin of the eyelids and adjoining parts. 5. In entom., the border surrounding the compound eye of an insect, especially when it forms a raised ring, or differs in color or texture from the rest of the head. In Diptera the different parts of this border are distinguished as the anterior or facial orbit, the inferior or genal, the posterior or occipital, the superior or vertical, and the frontal, according to the regions of the head of which they form a part. When not otherwise stated, orbit generally means the inner margin of the eye, or that formed by the epicranium. - Equation of the orbit. See equation. Inclination of an orbit. See inclination. - Orbits of the ocelli, those portions of the surface of the head immediately surrounding the ocelli or simple eyes. orbita (ôr'bi-tä), n.; pl. orbitæ (-tē). [L., orbit: see orbit.] 1. In ornith., the cir cum orbital region on the surface of the head, immediately about the eye.-2. In an at. and zoöl., the orbit or bony socket of the eye. orbital (ôrbi-tal), a. [= F. orbital = Sp. orb i tal = It. orbitale; as orbit + -al.] In zoöl. and an at., of or pertaining to the orbit of the eye; orbitar or orbitary; cir cum ocular. Orbital angleuthe angle between the orbital axes. Also called bi orbital angle. Orbital arch, upper margin the orbit. - Orbital artery, a branch of the superficial (sometimes from the middle) temporal artery distributed about the outer canthus of the eye. - Orbital bone, any bone which enters into the formation of the orbit. - Orbital canals (distinguished as anterior and posterior internal ), canals formed between the ethmoid and the frontal bone, the anterior transmitting the nasal nerve and the anterior ethmoidal ve els, the posterior the posterior ethmoidal ve els.-Orbital convolutions. Same as orbital gyri (which see, under gyrus ). - Orbital fo a, in crustaceans, the groove or fo a in which the eye-stalks of a stalk-eyed crustacean can be folded or shut down like a knife-blade in its handle. - Orbital gyri. See gyrus. - Orbital index. See craniometry. - Orbital lobe, the anterior lateral division of the carapace of a brachyurous crustacean. - Orbital nerve, any nerve which enters or is situated in the orbit; specifically, a branch of the supramaxillary or second division of the fifth cranial nerve, given off in the sphenomaxillary fo a, entering the orbit by the sphenomaxillary fi ure, and dividing in the orbit into temporal or malar branches. Also called tempo rom alar nerve. - Orbital plate. (a) The os planum or smooth plate of the ethmoid bone, which in man, but not usually in other animals, forms a part of the inner wall of the orbit. (b) The thin horizontal plate of the frontal bone on both sides forming the roof of the orbit. - Orbital proce , a proce of the palate-bone which in man enters to a slight extent into the formation of the orbit. - Orbital sulcus. See sulcus. Orbital vein, a vein receiving some external palpebral veins, communicating with the supra-orbital and facial veins, and emptying into the middle temporal vein. orbitary (ôr'bi-ta-ri), a. [= F. orbitaire = Sp. Pg. orbita rio; as orbit + -ary.] Same as orbital; specifically, in ornith., cir cum orbital: as, orb i tary feathers.