Modern understanding of the phonology of East Semitic languages can only be derived from careful study of written texts and comparison with the reconstructedProto-Semitic. Most striking is the loss of the glottal stop, or aleph, and the voiced pharyngeal fricative, or ayin, both of which are prominent features of West Semitic languages (for example, Akk.bēl 'master' < PS.*ba‘al). Also, East Semitic languages do not possess a series of three back fricatives: *h, *ḥ, *ġ. Their elision appears to give rise to the presence of an e vowel, where it is not found in other Semitic languages (for example, Akk.ekallu 'palace/temple' < PS.*haykal). It also appears that the series of interdental fricatives became sibilants (for example, Akk.šalšu 'three' < PS.*ṯalaṯ). However, the exact phonological make-up of the languages is not fully known, and the absence of features may have been the result of the inadequacies of Sumerian orthography to describe the sounds of Semitic languages rather than their real absence.