This point is known as the node of Ranvier.

These, like the two upper octaves of the flute and the harmonics of the violin, are produced by the column of air dividing itself into two vibrating halves, with a node between them; while the open chest notes of the human voice and the lower octave of the flute are produced by the undivided column of air vibrating as a whole.

When we had made ourselves smart for dinner and joined Miss Lavinia by the fire in her tiny library, we read by her hair that she was evidently intending to stay at home that evening, for her head has its nodes like the moon.

[Footnote 1: There are two simple leaves at the next node to the cotyledons; after these there is one compound leaf at each node.