Now that music began taking a more definite rhythmic form than before, a more regular dividing off of the phrases became necessary. This was accomplished by the use of a dot, and another form, the perpendicular line, which we have noticed in the song of the King of Navarre (1250). At first a means to indicate triple time was invented, and the measure corresponding to our [9/8] was indicated by placing the sign [O.] at the beginning of the line. This was called perfect. Then, for plain triple time the dot was omitted [O]; for [6/8] time the sign [C.] was adopted, and for ordinary common time [C] was taken. Consequently, when these signs were placed at the beginning of the line they changed the value of the notes to correspond to the time marked. Thus in [O.] (_tempus perfectum_, _prolatio major_) or [9/8], the _brevis_ was reckoned worth three _semibrevi_ [B = S S S] ([1. = 4. 4. 4.]); the _semibrevis_ three _minimi_ [S = M M M] ([4. = 8 8 8]). In [O] or [3/4] time [B = S S S] ([2. = 4 4 4]); but the _semibrevis_ was only as long as two _minimi_ [S = M M] ([4 = 8 8]). In [C.] or [6/8] time [B = S S] ([2. = 4. 4.]), but [S = M M M] ([4. = 8 8 8]). In [C] or [2/2] time [B = S S] ([1 = 2 2]), and [S = M M] ([2 = 4 4]). In the beginning of the fifteenth century the notes began to be written in an open form [Illustration] _Maxima_. [Illustration] _Longa_. [Illustration] _Brevis_. [Illustration] _Semibrevis_. [Illustration] _Minima_. [Illustration] _Semiminima_, which was added later. As still smaller units of value were added, the _semiminima_ was replaced by [filled minima], and the half _semiminima_ thus became [minima with tail], and the next smaller values, [two tails] and [three tails]. The rest to correspond to the _semiminima_ was [illustration]; for the _semibrevis_ [illustration], and _minima_ [illustration]. Thus we have the following values and their corresponding rests: _Maxima_ [Illustration] _Longa_ [Illustration] _Brevis_ [Illustration] _Semibrevis_ [Illustration] _Minima_ [Illustration] _Semiminima_ or _crocheta_ [Illustration] _Fusa_ or _crocheta_ [Illustration] _Semifusa_ [Illustration] The rests for the _fusa_ and _semifusa_ were turned to the left in order to avoid the confusion that would ensue if the rest [illustration] stood for [fusa]. Besides, the sign would have easily become confused with the C clef [illustration].