A Comparison of the mammalian and reptilian tecta

Abstract

FIQURESAlthough the present group of papers is concerned chiefly with the te,mental and isthmus regions of the midbrain, a brief r6sumQ of the tectal pattern in mammals, with comparisons with that seen in reptiles, may not be amiss.This is more particularly true since the part of this series of papers dealing with the fiber paths of the midbrain is introduced by a detailed account of many of the tectal connections in a wide range of mammals.Moreover, an understanding of the significance of the mammalian pattern is facilitated by a comparison of it with that seen in submammalian brains. STRATA O F THE MAMMALIAN OPTIC TEGTUMLike other regions in the nervous system, the mammalian optic tectum has been subdivided differently by various observers, depending upon the animals studied and the particular relations the worker was seeking to emphasize.I n the present account, a nine-layered pattern, similar to that described by Tsai ('25) for the marsupial, has been used as a basis for description.Table 1 is a summary of the chief eharacteristics of the layers of the superior collicular portion of the tectum in certain representative mammals, as revealed in toluidin blue, pyridine silver and Weigert preparations.These layers are illustrated in figures 1 to 3 and figures 7, 9 and 10 for the mammals indicated in the figure descriptions.