The origin of the Corpus Callosum, a contribution 

 upon the Cerebral Commissures of the Vertebrata'. 



By 



Dr. Henry F. Osborn, 



Professor of Comparative Anatomy, Princeton College U. S. A. 



With plates XIII, XIV and 2 figures. 



In the lamina terminalis of the brain of the Amphibians and 

 of most Reptiles and Birds are found two commissures which con- 

 nect the Cerebral hemispheres. The lower of these passes lateral- 

 wards into the brain stem; the upper bends upwards and forwards 

 passing- above or in front of the foramina of Monro into the inner 

 mantle. A division has long been known to exist in the anterior 

 commissure of the mammalian brain into two parts, known respec- 

 tiorly as the Pars olfactoria and Pars temporalis and it is generally 

 held that the upper and lower commissures in the sub - mammalian 

 orders correspond respectively to these two parts of the mammalian 

 anterior commissure. It is the object of this paper to show that the 

 upper commissure in the Amphibian and Sauropsidan brain represents 

 the corpus callosum while the lower commissure represents the an- 

 terior commissure. 



1 Obgleich das Morphologische Jahrbuch nur zur Publikation deutsch ge- 

 schriebener Artikel bestimmt ist, glaubte der Herausgeber in der Aufnahme 

 dieses Artikels im englischen Originaltext eine Ausnahme machen zu dürfen, 

 für welche es dem Interessentenkreis des Jahrbuches gegenüber wohl keiner 

 besonderen Rechtfertigung bedarf. 



