Editing Midbrain (section)

==Development==
{{Further|Isthmic organizer}}
[[File:Human embryo 8 weeks 4.JPG|thumb|Mesencephalon of human embryo]]

During [[embryonic development]], the midbrain (also known as the mesencephalon) arises from the second [[brain vesicle|vesicle]] of the [[neural tube]], while the interior of this portion of the tube becomes the cerebral aqueduct. Unlike the other two vesicles – the [[forebrain]] and [[hindbrain]] – the midbrain does not develop further subdivision for the remainder of neural development. It does not split into other brain areas. While the forebrain, for example, divides into the [[telencephalon]] and the [[diencephalon]].<ref>Martin. Neuroanatomy Text and Atlas, Second Edition, 1996, pp. 35-36.</ref>

Throughout embryonic development, the cells within the midbrain continually multiply; this happens to a much greater extent ventrally than it does dorsally. The outward expansion compresses the still-forming cerebral aqueduct, which can result in partial or total obstruction, leading to congenital [[hydrocephalus]].<ref>{{cite web |url=http://www.ninds.nih.gov/disorders/hydrocephalus/detail_hydrocephalus.htm |title=Hydrocephalus Fact Sheet |publisher=National Institute of Neurological Disorders and Stroke |date=February 2008 |access-date=2011-03-23}}</ref> The tectum is derived in embryonic development from the [[alar plate]] of the neural tube.