The mandibular joint in ten marsupials and monotremes is described.
No dise was found in Dasyurus. In Tuchyglossus, Ornithorhynchus and Sarcophilus fine fibrous strands were observed which are assessed to be remnants of discs. Larger segments of discs were observed in both joints of Macropus. Didelphys and Metachirus presented complete discs which were attached to the joint surfaces. All other joints presented complete discs, free from the articular surfaces.
In joints without discs or opposite gaps in discs, the articular, membranes were thick. Comparison is made to similar appearances in rabbits following surgical removal or damage to the disc.
The significance of the variations in the morphology of the discs and articular membrances is discussed.