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"Varimax rotation. Reproduced with permission from Jerison (1991).

"Varimax rotation. Reproduced with permission from Jerison (1991).

volume in these five species (logarithmic measures; r = 0.999). Developmental and morphological evidence obtained by B.L. Finlay and her associates, essentially supporting the conclusions of the factor analysis, has resulted in much more extensive additional evidence for the fundamental uniformity of structure in the mammalian brain, that is, for the extent to which it ''hangs together.''

The second factor in Table I, accounting for 12.7% of the variance, is an olfactory bulb factor. It is represented primarily by the olfactory bulbs, with a modest representation in the parts of the brain that are classic ''rhinencephalon'' (piriform lobes, schizocor-tex, and hippocampus) and in body weight. Factor analyses are notoriously susceptible to artifacts of sampling, and I believe that the high fraction of variance accounted for by the olfactory bulb factor is such an artifact. Simian primates have much reduced olfactory bulbs, whereas insectivores are normal mammals in this regard. The distribution of olfactory bulb size in the sample on which the factor analysis was performed is, therefore, seriously bimodal. This inflates the measured variance of the size of the olfactory bulbs and enlarges its fraction of the total variance compared to what would be expected in a more representative sample of mammals. In any case, the important feature of the multivariate analysis is the almost uniformly heavy loadings of the other measures on the general size factor.

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