Thompson, Brains of Cerehratulus. 



645 



TABLE OF COMMISSURES. 



Dorsal Cojnmissure. — The dorsal commissure, fig. i, D C, 

 curves forward and also upward, encircling the proboscis at its 

 point of attachment, but the latter curve is not represented in fig. 

 I, which is approximately in one horizontal plane. From its most 

 anterior point to its posterior ending in the dorsal lobes the dorsal 

 commissure is present in ten sections, and the dorso-ventral mea- 

 surement is yofi. Upon the surface of the commissure ganghon 

 cells of type I are very abundant, and a few are found within, 

 between the fibers. 



First ventral commissure.— The fiTStventral commissure, fig. i, F^y 

 is the stoutest commissure in the brain, measuring i6o/< dorso- 

 ventrally, and eighteen sections in thickness. Its surface is closely 

 invested with a layer of ganglion cells of type I, and great clusters 

 of cells of types II and UI are present in the outer part of the 

 cellular sheath, especially on the ventral side. 



Second ventral commissure. — The second ventral commissure, 

 fig. I, 2, is situated thirty-three sections posterior to the first. The 

 thickness is two sections, and the dorso-ventral measurement is 



