Table 1.

Ways in which the neural tube can fail to form.

Lack of convergent extension

Lack of medial hinge point (MHP) 1

Lack of dorsolateral hinge point (DLHP) 1

Lack of neuroepithelial bending by apical constriction (cranial region)

Lack of structural integrity of the neuroepithelium

Lack of support from surrounding mesenchyme Lack of midline fusion of neuroepithelium and/or surface ectoderm Interference by excessive anterior-posterior curvature of the neural plate

¹ Shown in Figure 2.