Forms with the initial sibilant, whose primary nature cannot be doubted in view of the data of non-Semitic Afroasiatic languages, are found in Akk. and, to a greater or lesser extent, in MSA. In Ug., Heb., Arb. and Sab. *š- shifts to h- (Kogan 2009:66).
No convincing explanation of the loss of the initial *h has been suggested. The deictic extension *-tī has parallels in other pronominal forms (for example, Geez zātti). See Bulakh–Kogan 2013b:98.