Bony Orbital Anatomy of the Koala (Phascolarctos cinereus)
Kempster, RC & Hirst, LW 2002, The Anatomical Record, vol. 267, pp. 288-291.
This study was the first to document anatomical details of the normal koala orbit, which showed consistencies in the overall orbital structure compared with other marsupials. This information can be used to improve understandings of the koala’s anatomy and aid research efforts to find treatments for ocular disease in the koala.
The analyses of orbital bones were performed on koalas that were already deceased or had to be euthanised as a result of trauma or illness. Descriptions of the orbital bones were recorded from macerated skulls that were boiled and cleaned. The results obtained by this study show similarities between some foramina of carnivorous polyprotodont and herbivorous diprotodont marsupial species, despite the fact that the koala has a contrasting ‘frontal’ appearance. Similar features of the koala orbital anatomy to other marsupials include the common optic-orbital fissure, through which important anatomical structures pass and can consequently be damaged during orbital trauma. In addition, the rostral alar foramen is similar to those exhibited in polyprotodont marsupials (such as the bandicoot) where it serves to convey the maxillary division of the trigeminal nerve but not transmit any blood. The lacrimal bone structure was also similar to other marsupials; however, the nasolacrimal system of the koala was not as complex as seen in humans and domestic animals such as cats and dogs. This may cause the spread of infections to the eye, as captive, stressed koalas typically sniff their surroundings. The study also shows that like most marsupials, the koala exhibits an open orbit with a muscular orbital floor and does not need a bony protective roof as it does not engage in any type of combat that may result in damage to the upper eye.
The findings of this study provide baseline data for future studies of the koala orbital anatomy, which inform our understanding of ocular disease in the species. At the time of this study, implications of the positioning and communication between some orbital features such as the rostral alar foramen need to be studied in more detail.
Summarised by Robyn Boldy
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