CEREBRAL COMMISSURES IN THE VERTEBRATA. 



457 



Sorenson's critical review * of the enormous mass of literature which is devoted to this 



Fig. 1. 



region of the brain 



pUcIV. 



hyp. 



A mesial sagittal section of tlie brain of an embryo [Deudy's stage S] of Hi>lur,wdon puitcbttion. Magnified almost 



10 diameters. Outline drawn with camera lucida. 



The cerebral hemisphere and the anterior quadrigemiual body, which, of course, are not seen in a mesial section, 



are also represented ; for explanation of abbreviations see page 500. 



,p.s. 



^"^'m^^i^^^^ 



Semi-schematic representation of the Roof of the Forebraiu in Sphemdon. Considerably enlarged from figure 1. 

 Camera lucida drawing. The commissura aherrans is immediately in front of the letter c. 



The structures just enumerated are foimd in almost all Vertebrates. But in the brain 

 of Spheiwdon there is another structure in close relationshij) with the roof of the third 



* A. D. Sorenson, " Comparative Study of the Epiphysis and Roof of the Diencephalon," Journ. Comp. Neurology, 

 vol. iv. (April 1894) pp. 12-72. 



67* 



