Orbital apex

The orbit is defined as the anatomic space in the skull that contains the eyeball and its accessory organs. At the orbital apex, many nerves and blood vessels pass from the orbit into the cranial cavity and vice versa. The orbit is pyramidal in shape, with four bony walls narrowing posteriorly toward the apex. 

The intraconal space is defined by the rectus muscles and their intercormecting septa. It contains the optic nerve, motor nerves, some blood vessels, and intraconal orbital fat tissue. Among the intraconal blood vessels, the ophthalmic artery, which branches off from the intracranial internal carotid artery, enters through the optic foramen. Near the orbital apex, the central retinal artery takes off from the ophthalmic artery and runs caudal to the optic nerve, whose dura mater it usually enters approximately 1 cm dorsal to the eyeball. 

The formation of a further single bond between sulfur and carbon, as in the trimethylsulfonium cation, may be pictured as involving a 3sp3 unshared pair orbital on sulfur and an empty 2sp3 orbital on carbon in a methyl cation. Thus the three a bonds and the remaining unshared pair (in a 3sp3 orbital) in a trialkylsulfonium ion are distributed approximately tetrahedrally, i.e. the ion is pyramidal, with the sulfur atom at the apex (2). 

A conglomerate of three hexagons contains one central atom and 12 atoms around it. A conglomerate of seven hexahedrons comprises 12 external and 12 internal (common) atoms. In these two cases geometric centers of hybridized molecular orbitals of each hexahedron are equidistant from such nearest centers of a conglomerate. This, apparently, explains the experimental fact that polyhedrons of carbon clusters represent an icosahedron - 12-apex crystalline structure each apex of which is connected with five other apexes. 

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