More than 2,000 data on volumetric measurements of 42 structures in a variety of up to 76 species (28 insectivores, 21 prosimians, 27 simians) are given. All volumes measured in serial sections were converted to fresh volumes of a brain having a standard size within a given species. The data are available to all scientists for comparison and analysis. To allow critical evaluation, details on fixation and preparation, on determination of fresh brain weights and volumes of brain parts and on intraspecific variability are given.

The degree of cortical folding in primates has been analyzed using a gyrification index (GI). Correlation analyses of the GI with body weight, brain weight and neopallial volume show that the human data fit the general trend of the nonhuman anthropoids. Bigger primate brains exhibit a higher degree of fissurization, but a taxonomic difference that is independent of brain weight between prosimians and anthropoids has also been observed. In these regressions, anthropoids differed from prosimians by having a larger increase in gyrification for every unit increase in body or brain weight or neopallial volume. A stepwise regression, also shows a prosimian-anthropoid difference. The best predictor for convolutedness in anthropoids is neocortical volume, while in prosimians it is brain weight. The GI in catarrhines is correlated with total sulcal length but not number of sulci. This result suggests paleontological studies of total sulcal length can give direct information on the evolution of cortical folding in primates.

Comparative architectonic studies have resulted in a classification of the amygdaloid complex which differs somewhat from the commonly used classification (first proposed by Humphrey, 1936) by separating the cortical amygdaloid nucleus from the centromedial group and assigning it to the basolateral group, which then forms a cortico-basolateral group. The size changes of these groups and of the nucleus of the lateral olfactory tract (belonging to the centromedial group) and the large-celled part of the basal nucleus (belonging to the cortico-basolateral group) have been investigated in representatives of an ascending primate scale. In all structural complexes investigated so far, the small-celled part of the cortico-basolateral group is the most progressive. In descending order of progression there follow: the cortico-basolateral group as a whole, the amygdala as a whole, and the large-celled basal nucleus. No clear changes were found in the centromedial group as a whole, whereas the size of the nucleus of the lateral olfactory tract, which represents a small component of this latter group, shows a strong reduction. These differences in the developmental trends point to increasing or decreasing capacities of the functional (limbic and olfactory) systems, to which these structures are related.

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The brain of the La Plata dolphin, Pontoporia blainvillei, was studied with methods of quantitative morphology. The volumes and the progression indices of the main brain structures were determined and compared with corresponding data of other Cetacea, Insectivora and Primates. In Pontoporia, encephalization and neocorticalization are clearly greater than in primitive ("basal") Insectivora. The indices are in the lower part of the range for simian monkeys. The paleocortex is regressive in accordance with the total reduction of the olfactory bulb and olfactory tract. In contrast to the situation in primates, the septum, schizocortex and archicortex are not progressive in Pontoporia. The striatum and cerebellum are strongly progressive, corresponding to the efficiency and importance of the motor system in the three-dimensional habitat. The diencephalon, mesencephalon and medulla oblongata show considerable progression. Obviously, this is correlated with the extensive development of structures of the acoustic system. The superficial correspondence of the brains of dolphins and primates in relative size and in the degree of gyrencephaly is rather a rough morphological convergence than a sign of functional equivalence. It is coupled to a strongly divergent development of the various functional systems in the two mammalian orders according to their specific evolution.