Fig. 2. Midline and rostral neural defects. (A-C) Neonate transverse sections. (A) Wild type showing anterior commissure (ac) and bilateral cerebral hemispheres (ch). (B) Midline mutant lacking anterior commissure (asterisk) and showing cerebral hemispheres fused into a holosphere (hs). (C) Truncation mutant lacking CNS rostral to hindbrain. (D,E) E13.5 transverse sections. (D) Wild type showing medial falx cerebri (fc). (E) Midline mutant shows a single rostral ventricle (asterisk). (F,G) E9.5 embryos. (F) Wild-type embryo shows lamina terminalis (lt) marked by Vax1 expression. (G) Midline mutant lacks lamina terminalis (asterisk). (H-J) Neonatal brains. (H) Wild type showing olfactory bulbs (ob). (I,J) Mild truncation mutant showing hypoplastic, fused olfactory bulbs (I) or lacking olfactory bulbs (J). (K,L) E10.5 embryos. (K) Wild type showing telencephalic vesicles (tv). (L) Midline mutant has single holospheric vesicle (hs). (M) Moderate truncation mutant lacks telencephalon (asterisk). (N) Severe truncation mutant lacks both forebrain and midbrain. mo, medulla oblongata; ov, optic vesicle; p, pons; cbl, cerebellum; m/h, midbrain/hindbrain boundary. Scale bars: 2 mm in A-C; 0.5 mm in D,E; 0.2 mm in F,G; 1 mm in H-N.