Noun. 1. optic disc-the point where the optic nerve enters the retina; not sensitive to light. optic disk, blind spot. retina-the innermost light-sensitive membrane covering the back wall of the eyeball; it is continuous with the optic nerve.
The mantle layer is the largest of the class. About half of our planetâs mass. The mantle is composed of very hot dense rocks, That move and flow, always on the go, they never lock, Extract from http://www.educationalrap.com/song/layer...
The thickest layer of the Earth. January 17, 2015January 15, 2015 Mihai Andrei. The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core and the inner core.Out of them, the mantle is the thickest layer, while the crust is the thinnest layer.he thickest layer of the Earth. January 17, 2015January 15, 2015 Mihai Andrei. The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core and the inner core.