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Introduction: The present study is a case report of a male 6 days old layer chick from a commercial breeder that attracted attention because it featured an additional pair of legs attached to the caudal part of the body. The chick was submitted to computed-tomography (CT) examination and subsequent anatomical dissection.
Results: Apart from the obvious supernumerary limbs, the dissection revealed additional malformations of the hind gut: three unifom-sized ceaca flanked the ileum, and the colorectum branched and continued into paired cloacae that were situated on the left and right dorsolateral aspect of the body, respectively. While the right cloaca was continuous and contained both faeces and urine, the proctodaeum of the left cloaca was clotted and the cloaca contained mainly inspissated urine. The supernumerary legs were attached to the curtate pygostyle via cartilage and skin. The additional legs featured a prominent unpaired osseous component that most likely corresponds to fused femoral anlagen, as well as paired tibiotarsi, tarsometatarsi and four digits that resembled ?normal? leg anatomy even if they were only in part actively mobile and less distinct than the ?normal? legs of the chick. Additionally, two separate bones attached to the caudo-ventral aspect of the regular ischiadic bones - presumably residual hip bones - were developed. The supernumerary legs were supplied by paired major vascular and nerval branches originating from the respective sacral trunks of the body. One paired major muscle originated from the ischiadic bones and terminated at the proximal tibiotarsus of the surplus legs. The findings of the dissection verified the results of the CT examination. A PC-based three-dimensional reconstruction of the osseous tissue from the CT datasets clearly depicted all bony components of the additional rudimentary hip and the supernumerary leg bones.
Discussion: CT examination and three-dimensional reconstruction is a helpful tool to demonstrate and identify the osseous components of malformed or surplus body parts. A hypothesis on the possible embryonic morphogenesis of the reported malformations is suggested.