Army Medical Staff Corps
This button, with Queen Victoria’s cypher and crown, is from the British Army. The Medical Staff Corps was first raised in 1855, only to be renamed Army Hospital Corps in 1857 then re-re named the Medical Staff Corps in 1884. Until 1870 the various British troops in Australian were cared for by regimental surgeons and colonial surgeons. The first regular Australian Army surgeon was Dr W. J. Bedford, appointed in 1871. The backmark dates to around 1887-1901; it may not have been worn in Australia.
http://australianmilitarymedicalcollective.weebly.com/army-medical.html
The Port Macquarie Museum has a fine example of Royal Army Medical Staff c.1830. The buttons have a William IV cypher but a similar design. See https://ehive.com/collections/3977/port-macquarie-museum
George V NSW Tranways in nice condition
AMF button
This has no makers mark, and a different type of shank. I like the squished Arnhem Land, and the very pointy Cape York. For other examples, see the military uniforms page. http://www.austbuttonhistory.com/defence-forces-uniform-buttons/1901-ww2/