In the developing chordate (including vertebrates), the<unk>  is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The<unk>  groove gradually deepens as the<unk>  folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into the closed<unk> . In humans,<unk>  closure usually occurs by the fourth week of pregnancy (the 28th day after conception). The ectodermal wall of the<unk>  forms the rudiment of the nervous system. The centre of the<unk>  is the<unk>  canal. Stages of<unk>  formation.
Neural tube
Embryoid body
Cervical cap
Embryocardia
Germinal matrix
Breast shell
Wound
Kidney dish