. Bulletin - American Museum of Natural History. Natural history; Science. 2IO Bulletin American Museum of Natural History. |Vol. VII, Sexual Variation.—The skulls of males are generally larger than those of females of corresponding age, and more heavily ossified, but in other respects there seems to be no very apprecia- ble difference. Individual Variation.—In skulls of the same sex, and appar- ently of the same age, there is quite a range of variation in size, so that large females may exceed the dimensions of small males. Thus in old males from Fairbank the length of the skull varies from 3
. Bulletin - American Museum of Natural History. Natural history; Science. 2IO Bulletin American Museum of Natural History. |Vol. VII, Sexual Variation.—The skulls of males are generally larger than those of females of corresponding age, and more heavily ossified, but in other respects there seems to be no very apprecia- ble difference. Individual Variation.—In skulls of the same sex, and appar- ently of the same age, there is quite a range of variation in size, so that large females may exceed the dimensions of small males. Thus in old males from Fairbank the length of the skull varies from 38 to 42 mm., and the zygomatic breadth from 24 to 26 mm.; in old females from the same series the length varies from 36 to 39 mm., and the breadth from 22 to 24 mm. The width of the nasal bones, and correlatively the width of the rostrum, varies considerably in individuals of the same sex and age. But the most variable feature is the size and form of the interparietal, which may be twice or three times as large in some specimens as in others. While usually quadrate, and nearly as long as wide, it may be more or less convex on the posterior border, or, in rare cases, regularly convex anteriorly from the nearly straight posterior border. As these variations (see Figs. 3-8) occur in each of the large series at hand, and in about the same proportion, they cannot be considered as other than indi- vidual. In probably 75 per cent, the interparietal is distinctly four sided, with nearly straight outlines, except for a tendency. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original American Museum of Natural History; Allen, J. A. (Joel Asaph), 1838-1921. New York [American Museum of Natural History]
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