CEREBRALISATION UND ONTOGENESEMODUS BEI EUTHERIEN

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Abstract
The various methods for the determination of the degree of cerebralization may be classified into 2 categories; one depends upon the comparison of brain- and body weight, the other upon the comparison of parts of the brain which possess 2 different levels of evolution. The indices for the entire brain and for such parts of the brain as neopallium-olfactory brain, cerebellum and brainstem are presented for each type. The degree of cerebralization of the analyzed types is compared with the classification by the systematic method and that used by palaeontologists. The degree of cerebralization equal to that of the human-being is attained by the dentate whale. Man, Odontoceti and Elephant form the group of the highest order. Their indices greatly surpass those of the middle-order groups. The bearded seal, Pinnipedia and Simia assume the highest positions of the middle group. Some Cebidae have attained the niveau of cerebralization of the Pongidae. Hoofed animals with the highest degree of cerebralization are the Hippomorpha on the one hand and the Giraffidae on the other. The level of cerebralization of the Bovidae is relatively low. Bears are the most developed carnivores. Behind them are the Felidae and not the Canidae. The descending order of cerebralization for the rodents is as follows: Pentalophodonta, Non-Pentalophodonta and Myodonta. The differences of the degree of cerebralization within the Insectivora are greater than those which separate these most primitive Eutherians from the half-apes. The multiplication factor of the brain, i.e. that number which indicates how much the brain weight of the newborn increases in order to attain the weight of the adult brain, is the single criterion which allows a definite division of mammals into heterophagi and autophagi. The most significant values are afforded by the multiplication factors of the cerebellum. They lie below 4.9 for the autophagi and are between 12.9 and 106 for the heterophagi. The low-order mammals may be autophagi or heterophagi, the high order of mammals are always autophagi. Of the closely related types and families, those which exhibit more of the heterophagous characteristics are always less cerebralized. Bears, the most extreme heterophage of the mammals, constitute the single exception. During evolution the transition from heterophage to autophage precedes the increase in the degree of cerebralization.