In the present paper we will examine a number of graphotactic rules which emerge from an analysis of several graphemic alternations, observed in a delimited Turkic text corpus in Brāhm-i script. This analysis will lead us to propose a possible reconstruction of the phonemic dorsal system denoted by the linguistic domain here considered: such a system is intended to be effective exclusively within this specific domain. In particular, we will examine the graphophonemic status of the akṣaras usually transcribed as ‹qa› and ‹g1a› within the Northwestern Brāhmī script system, as they occur both in Tokharian and Turkic scribal practice. Though our primary goal is the consistency of the proposed reconstruction, rather than its historical soundness, we will eventually argue that, within the dorsal system here described, no ‘voiced’–‘voiceless’ opposition is retrievable.