Monocephalus omphalopagus (tetrabrachius tetrapus) in a lamb

Caudal duplication is an abnormality which usually affects the digestive, urogenital and even respiratory systems. It forms a graded series from slight duplication to near separation of two fetuses caudocranially. In some conjoined twins, duplication process may cranially proceed up to the head region. This kind of developed conjoined monocephalus twin has been reported in many domestic species and is classified as thoracopagus or omphalopagus twins according to the presence of one or two hearts, respectively. A male dead conjoined monocephalus twin lamb attached from neck to thorax was used for this study. Lateral and dorso-ventral digital radiography and anatomic dissection were performed on the case. The results showed that duplication process of the gastrointestinal tract interestingly prevented cranial to the midgut, while more cranial organs such as heart, lungs and even brain were seen duplicated. Duplication anomaly has been mostly reported cranially in cattle and caudally in sheep. Nevertheless, if duplication process does not occur completely, some body organs of the resulting conjoined twin will remain unduplicated. Duplication process of this case is thought to strengthen Spencer’s spherical theory.