In 1963, Binns et al. [1] described the development of congenital cyclopean-type malformations in lambs following maternal ingestion of the range plant Veratrum californicum (Durand). While cattle, sheep, rat, and rabbit embryos under such conditions develop mainly cyclopia, chicken embryos preferentially develop holoprosencephaly [1-4]. Holoprosencephaly is a developmental field defect of impaired midline cleavage of the embryonic forebrain (for reviews, see [5] and [6]). However, there is a wide phenotypic spectrum depending upon the specific cause of this malformation. In its most extreme form, it is associated with cyclopia, which is characterized by one eye being located centrally over the root of the nose (l " Fig. 1). In sheep such effects occur when pregnant ewes are exposed on day 14 of gestation. The most frequent defects caused by exposure at later periods of gestation, around day 30, are limb deformities, palate defects, and severe tracheal stenosis [7]. All these defects in

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