As regards the transition from the Lower Thin to the Upper Thin, I would suggest the following explanation:--The vocal chink is at first, as Madame Seiler says, linear, and the gradations of tone are caused by simple tension of the vocal ligaments, which is proved by the diminution of the ring-shield aperture. While this goes on we are in the Lower Thin. Now the laryngoscope reveals another method of still further raising the pitch, which consists in a gradual shortening of the vocal chink. This is caused by the shield-pyramid muscles pressing together the ends of the vocal ligaments, thereby giving the vocal chink a slightly elliptic shape. When this mechanism comes into play we are in the Upper Thin. THE SMALL REGISTER. "When in the observation of the thin register I had sung upwards to its highest tones, and then sang still higher, I became aware, with the F[#] [Illustration: musical notation] of a change in the motions of the organ of singing, and the tones thus produced had a different _timbre_ from those of the Thin. It required long and patient practice before I finally succeeded in drawing forward the lid so that I could see the glottis in its whole length. Not until then was I able to observe the following: With the F[#] [Illustration: musical notation] the vocal ligaments suddenly closed firmly together to their middle, with their fine edges one over the other. This closing appeared as a fine red line extending, from the pyramids at the back, forward to the middle of the vocal ligaments, and leaving free only a third part of the whole glottis, immediately under the lid, to the front wall of the voicebox. * * * * * "The foremost part of the glottis formed an oval orifice, which, with every higher tone, seemed to contract more and more, and so became smaller and rounder. The fine edges of the vocal ligaments which formed this orifice were alone vibrating, and the vibrations seemed at first looser, but, with every higher tone, the ligaments were more stretched." * * * * * I have repeatedly had the opportunity of observing the mechanism of the small register, and I only differ from Madame Seiler in this, that I did not notice that "with every higher tone the ligaments were more stretched." It appeared to me, on the contrary, as though the raising of the pitch was produced by a contraction of the vocal ligaments. In all other respects I entirely agree with the above description. According to Madame Seiler the small register is formed by the action of the wedges, as described on p. 54.