Anthropoid or simian primates are of increasing interest for experimental brain research, since they are the nearest relatives to man. The supply of simian primates, however, becomes more and more difficult and breeding is advisable. In the larger species this breeding is an expensive and protracted procedure. A shorter time of development and a somewhat higher rate of reproduction is found only in the small marmosets. They produce in general more than one litter a year, each of which usually consists of two young ones. Beside this practical consideration, there are some other reasons which recently have induced several students to focus their interest on Callithrix. The common marmoset is one of the most primitive simian primates in respect to brain development (Stephan, 1967; Bauchot and Stephan, 1969) and complexity of behavior (for ref. see Lipp, 1978). This species and its brain may serve as a useful model for comparative morphological and behavioral investigations in primates. Cortical maps based on regional differences in the cytoarchitectonics were given by Brodmann (1909) and by Peden and Bonin (1947), and a brief stereotaxic atlas by Pecci Saavedra and Mazzuchelli (1969).