Perosomus elumbis, an infrequently encountered congenital anomaly of unknown etiology, was studied in a female Holstein calf. This error of morphogenesis represents a set of multiorgan malformations that produce a deformity of the caudal one third of the fetus. In this case, the spinal and pelvic malformations were radiographed and then dissected. Intra-abdominal abnormalities of the soft tissues are also described. The normal sequential embryologic development of the vertebrate skeleton, anterior-posterior fetal positioning, and neural tube migration are discussed. An extensive literature of this birth defect in cattle (and sheep) is reveiwed. The reports from a period covering 165 years are compared with the pathologic features in this case. Chromosomal aberrations within the homeobox gene family are postulated to be contributory factors in the development of this type of dysorganogenesis.