The Pratiçakhya Sutra of the Rigveda is an extensive metrical work in three books, traditionally attributed to Çaunaka, the teacher of Açvalayana; it may, however, in its present form only be a production of the school of Çaunaka. This Pratiçakhya was later epitomised, with the addition of some supplementary matter, in a short treatise entitled Upalekha. The Taittiriya Pratiçakhya is particularly interesting owing to the various peculiar names of teachers occurring among the twenty which it mentions. The Vajasaneyi Pratiçakhya, in eight chapters, names Katyayana as its author, and mentions Çaunaka among other predecessors. The Atharva-veda Pratiçakhya, in four chapters, belonging to the school of the Çaunakas, is more grammatical than the other works of this class. Metre, to which there are many scattered references in the Brahmanas, is separately treated in a section of the Çankhayana Çrauta Sutra (7, 27), in the last three sections (patalas) of the Rigveda Pratiçakhya, and especially in the Nidana Sutra, which belongs to the Samaveda. A part of the Chhandah Sutra of Pingala also deals with Vedic metres; but though it claims to be a Vedanga, it is in reality a late supplement, dealing chiefly with post-Vedic prosody, on which, indeed, it is the standard authority. Finally, Katyayana's two Anukramanis or indices, mentioned below, each contains a section, varying but slightly from the other, on Vedic metres. These sections are, however, almost identical in matter with the sixteenth patala of the Rigveda Pratiçakhya, and may possibly be older than the corresponding passage in the Pratiçakhya, though the latter work as a whole is doubtless anterior to the Anukramani. The Padapathas show that their authors had not only made investigations as to pronunciation and Sandhi, but already knew a good deal about the grammatical analysis of words; for they separate both the parts of compounds and the prefixes of verbs, as well as certain suffixes and terminations of nouns. They had doubtless already distinguished the four parts of speech (padajatani), though these are first mentioned by Yaska as naman, or "noun" (including sarva-naman, "representing all nouns" or "pronouns"), akhyata, "predicate," i.e. "verb"; upasarga, "supplement," i.e. "preposition"; nipata, "incidental addition," i.e. "particle." It is perhaps to the separation of these categories that the name for grammar, vyakarana, originally referred, rather than to the analysis of words. Even the Brahmanas bear evidence of linguistic investigations, for they mention various grammatical terms, such as "letter" (varna), "masculine" (vrishan), "number" (vachana), "case-form" (vibhakti).Still more such references are to be found in the Aranyakas, the Upanishads, and the Sutras. But the most important information we have of pre-Paninean grammar is that found in Yaska's work.