Brain phenotype of compound heterozygous Pax5 (+/−) Krd (+/−) mice. The entire brain (dorsal view in A, D, G, and J), a close-up view of the cerebellum and colliculi (B, E, H, and K), and histological sections of the midbrain and cerebellum (C, F, I, and L) are shown for 4-week-old mice of the genotypes indicated to the left. The sagittal plane of sectioning was close to the midline. Open arrowheads highlight the lateral displacement of the inferior colliculi in Pax5 (+/−) Krd (+/−) mice (G and H); a solid arrowhead indicates the intraculminate fissure present in the cerebella of these mice (I). Arrows point to the absence of the inferior colliculus in the lateral midbrain (J and K) and at the midline (L) of severely affected Pax5 (+/−) Krd (+/−) mice. SC, superior colliculus; IC, inferior colliculus; V, vermis; H, hemisphere; Cu, culmen; D, declive; T, tuber vermis; P, pyramis; U, uvula.