Anatomical study of brachial plexuses of a koala, a Tasmanian devil, and a common ringtail possum.

Background: Marsupials have a narrower range of forelimb morphological features than placental mammals. It is hypothesized that this is due to a constraint in the reproductive biology of marsupials. The constraint is that newborn marsupials must crawl into their mother's pouch. However, anatomical knowledge of the brachial plexus in marsupials is scarce and has not been discussed. In the present study, the purpose is to examine the anatomy of the brachial plexuses of a koala, a Tasmanian devil, and a common ringtail possum and to discuss the brachial plexus of marsupials with reference to the previous reports.

Materials and methods: One adult koala (Phascolarctos cinereus) specimen, one adult Tasmanian devil (Sarcophilus harrisii), and one adult common ringtail possum (Pseudocheirus peregrinus) were used in this study.

Discussion: The ventral rami of C5, C6, C7, C8, and T1 formed the brachial plexus in all 3 marsupials. Each nerve branch differed by one segment among the 3 marsupials. Therefore, the brachial plexus was considered in the form of a few differences among marsupials.

Conclusions: Because of a quite difficulty of getting an opportunity for anatomical examination on marsupials, an accumulation of cases like the present study is needed for future quantitative and qualitative analyses of the brachial plexus pattern of the marsupials.