|Brain of human embryo of four and a half weeks, showing
interior of fore-brain. (Cephalic flexure visible at center
top.) ||subject #184 737 The mesencephalic flexure or cephalic
flexure is the first flexure, or bend, of the embryonic brain;
it appears in the region of the mid-brain. In human embryos it
generally occurs at the end of the 3rd week/beginning of 4th. By
means of it the fore-brain is bent in a ventral direction around
the anterior end of the notochord and fore-gut, with the result
that the floor of the fore-brain comes to lie almost
antiparallel with that of the hind-brain. This flexure causes
the mid-brain to become, for a time, the most prominent part of
the brain, since its dorsal surface corresponds with the
convexity of the curve. As a consequence, the cardiac plate,
which was previously anterior to the forebrain, approximates its
adult location in what will become the thoracic region. External
links  This article incorporates text from a public domain
edition of Gray's Anatomy.