Studies on the variation and correlation of skull measurements in both sexes of mature albino rats (Mus norvegicus var. albus) / by Shinkishi Hatai.

  • Hatai, Shinkishi.
Date:
[1907]
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Licence: In copyright

Credit: Studies on the variation and correlation of skull measurements in both sexes of mature albino rats (Mus norvegicus var. albus) / by Shinkishi Hatai. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Determination of the Means and Variability of the Several Measurements. In Table I are exhibited the means of the several measurements, the standard deviations, the coefficients of variation and the differences between the two sexes, with their respective probable errors. These values were determined by the usual biometric formulge (Davenport, 04). As one would expect, the mean values in the males are always higher than in the females. Since in the present investigation the total number of measurements of both sexes was not large, it is important to compare the differences between the sexes with the corresponding probable errors in order to see whether or not the differences here found are to be considered significant. Table I shows clearly that in all cases the differences are greater than three times the probable errors. The maximum difference occurs in the nasal bone; ten times the probable error, and the minimum occurs in the width of the cranium, five times the probable error. This indicates that the characters under consideration are really greater in the male. The maximum percentage differences occurs in the nasal bone (7.5 per cent) and minimum in the width of the cranium (1.4 per cent) while the remaining differences are nearly similar (3.1 per cent to 3.9 per cent). From the percentage differences here found it would seem probable that if we compared the mature male and female skulls having the same total length, the length of the nasal bone in the male would be longer than that in the female, and since the length of the entire skull depends on the combined length of the nasal bone and the fronto-occipital length, it would follow that the fronto-occipital length or the length of the cranium, would be less in the male than in the female. In order to test this conclusion in any individual case it is necessary to determine whether or not the total length of the skull and of the nasal bone on one hand, and the total length of the skull and fronto-occipital length on the other hand, are closely correlated. This point will be more fully discussed after the coefficients of correlation have been determined. (a) Range of variates and rate of increase of the various characters associated with changes in the size of the entire skull.—The two e.xtremes of the various characters, as well as the rate of increase of those characters associated with the increase in the length of the entire skull, is somewhat different according to sex as is shown in Table II. As is shown in Table II, the absolute range between the two extremes is always slightly greater in male than in female except in the case of the