While I am far from being a specialist on American Indian material culture, what I have learned is that these type accoutrements were more of a 'medicine' or talismanic sort of item. These are fashioned from what are termed 'hair pipes' in thier parlance, and in earlier times were actually made of dentalium (mollusk shells), most of these heavily traded from Northwest Indian tribes. Many of the beads and wampum shells used in other forms of accoutement came from trade through the Northeast, though some shells from this source were also used for 'hair pipes'.
By about the 1860s and especially during the Reservation Period, these hair pipes were being fashioned from bone, and actually while much was likely from buffalo, good volume began to come from livestock firms in Chicago and New York using cattle legbones. There was considerable demand for these and varying versions of these breastplates were made, not just by tribal peculiarity but personal adaption. Apparantly by WWI demand for these had waned (according to John C. Ewers, "Hair Pipes in Plains Indian Adornment", Smithsonian Bulletin 164, 1957, Anthropological Papers #50, pp.29-85).
It seems that these type breastplates became more of a traditional costume item used ceremonially later in the 20th century and are of course produced still commercially, while many are authentically created and used in Native American ceremony today.
While it does not seem that these would have been terribly effective in most combat instances, especially with the advent of firearms, it must be remembered that these were characteristically talismanic much in the way of the 'war shirts' which were often decorated with honors and charm type symbols.
Very nice example, and it is fantastic to see interest in the extremely important topic of Native American weaponry and material culture, which deserves far more attention here.
* Barry who can ever forget the great photo of you in the war bonnet!!~!
