Fig. 4. Tsg^-/-;Bmp4^+/- neonates display holoprosencephaly. (A-A') Lateral view of the heads of wild-type and Tsg^-/-;Bmp4^+/- newborn mice. Tsg^-/- or Bmp4^+/- are indistinguishable from wild type. The Tsg^-/-;Bmp4^+/- mutant lacks a mouth opening, has only one nostril, and the external ear has an abnormal setting. (B-B') Frontal sections through the snout region of the same neonates stained with Mallory's tetrachrome. The lack of nasal septum (ns) indicates holoprosencephaly. The lower jaw is reduced. gm, genioglossus muscle; lt, lower tooth; md, mandible; mu, muscle; nc, nasal cavity; sp, secondary palate; to, tongue; ut; upper tooth.