be carefully distinguished from the dots themselves. Occasionally in the more elaborate carvings the numbers from o to nineteen are expressed by faces. In the case of o the lower jaw is formed by a hand, and numbers over ten are expressed by the face assigned to the corresponding unit but with a fleshless jaw. Ten itself is the head of the death-god. Zero in the normal notation is expressed either by a hand or a figure shaped somewhat like a Maltese cross. The use of the zero is explained later. The Maya, like ourselves, were in the habit of expressing a high number by a succession of
figures which combined to form a numeral, but they did not employ the decimal system. Their system, when applied to the computation of time, was on the whole, but not entirely, vigesimal, and was as follows. Twenty days, or kin, formed a uinal, and the uinal thus corresponded to one of their months; but the next higher unit, the tun, consisted of eighteen uinal, and contained 360 days, being thus equivalent to a year minus the five uayeb days. Twenty tun made a katun (7200 days), and twenty katun went to another period of which the name is not known, but which is usually called a cycle (144,000 days). There are indications that a higher unit still was recognized, the so-called "great cycle," consisting of thirteen cycles (1,872,000 days). Each of these periods was expressed by an appropriate glyph,
