Molar (tooth) and a neck. The occlusal surface is rough and mostly flat, adapted for crushing and grinding plant material. The body is covered with cementum both above and below the gingival line, below which is a layer of enamel covering the entire length of the body. The cementum and the enamel invaginate into the thick layer of dentin. The opposite condition to hypsodont is called brachydont or brachyodont (from "brachys", "short"). It is a type of dentition characterized by low-crowned teeth. Human teeth are brachydont. A brachydont tooth has a crown above the gingival line and a neck just below it,
Development of the nervous system intellectual disability. The mammalian central nervous system (CNS) is derived from the ectoderm—the outermost tissue layer—of the embryo. In the third week of human development the neuroectoderm appears and forms the neural plate along the dorsal side of the embryo. The neural plate is the source of the majority of neurons and glial cells of the CNS. A groove forms along the long axis of the neural plate and, by week four of development, the neural plate wraps in on itself to give rise to the neural tube, which is filled with cerebrospinal fluid (CSF). As the embryo develops, the