This essay represented an attempt to lay the foundations of a future critical edition relating with the polyphonic repertory of the origins, based on a new hypothesis of notation reading. It is maintained that the XIIth century neumatic writing must be interpreted by subtraction, i.e. considering as weak all the sounds placed at the beginning of every "neuma", and resting the rhythmical scanning on the "perfectio" which is invariably placed on the last sound. The aim of this study is: to take a step forward in comparison with the two previous editions of repertory, those of Theodore Karp and of Hendrik van der Werf; to try to fix some new scientific standards as regards about the study and the analysis of the neumatic groups; at last, to propose a series of inedited links with the theory of rhythmical modes and with the mensural notation of the successive centuries. The work consists in the analysis of the entire handwritten tradition of the two pieces best testified in the so called Aquitanian repertory, i.e. "Noster cetus" and "Omnis curet homo". It tries to define a first form of critical text and to value jointly all the textual variants reportet by the sources. The fundamental consequence of the starting task is the employment of a special type of notation, called "notazione breviata", which draws inspiration from the very first mensural solutions adopted around the half of the XIIIth century.