The diencephalon of the opossum in stereotaxic coordinates. I. The epithalamus and dorsal thalamus

Abstract

AbstractThis investigation consists on the identification of diencephalic cellular groups in the opossum and their fit to a standard brain. A statistical survey of the stereotaxic coordinates of neuroanatomical landmarks (commissura anterior, commissura posterior, nucl. habenulae medialis, sulcus striopallialis and the pedamentum) from coronal sections of brains of 19 South American (D. aurita) and four North American opossums (D. virginiana) was first performed. Speical precautions were taken to obtain sections at planes parallel to those of the stereotaxic instrument, or to ensure that any deviation thereof was accounted for in the measurements. The reconstruction of the standard brain is based on average coordinates from landmarks of the South American species. Estimates of the S. D. of each set of coordinates give a scatter no larger than 0.8 mm and as small as 0.1 mm from the average.Identification and outlining of nuclei and main fiber tracts was achieved from the study of three series of the aurita species cut in coronal sections and one in horizontal, adjusted to the coordinates of the standard brain. Inter‐ and intraspecies adjustments are made possible by correlating certain reference points with craniometric or body weight measurements.Thirteen representative figures provide the core of this work, together with a brief description of cellular groups pertaining to the epithalamus and dorsal thalamus. Data on the ventral thalamus and hypothalamus is given in a second paper (Oswaldo‐Cruz and Rocha‐Miranda, '67).