648 Journal of Comparative Neurology and Psychology. 



to originate in the cellular sheath of the left ventral lobe, hence this 

 commissure may be designated as a brain commissure, derived on 

 the left side from both fibrous core and cellular sheath, but on the 

 right side from the cellular sheath only. 



Eighth ventral co?nmissure. — The eighth ventral, fig. I, 8, is 

 the second commissure between the oesophageal nerves. It lies 

 two sections behind the seventh; the central part is two sections 

 thick, with a dorso-ventral measurement of 50«. Owing to the 

 opening of the roots into the oesophageal nerves three or four 

 sections posterior to the central part, the commissure has the 

 form of a broad curve. 



Ninth ventral commissure. — The ninth ventral commissure, 

 fig. I, 9, is only one section posterior to the eighth. The central 

 part is present in four sections, and measures dorso-ventrally 52/i. 

 Its most median portion is considerably thicker in an antero- 

 posterior direction than the lateral parts near the nerves. Like 

 the eighth, this commissure forms a broad curve, owmg to the 

 posterior position of the roots. The fibers pass beneath the 

 oesophageal nerves and may be traced in part into the fibrous core, 

 in part into the cellular sheath of the ventral brain lobes. There 

 is an intimate relation between the fibers of the roots of this com- 

 missure and those of the tenth, which will be described below. 



Tenth ventral commissure. — The central part of the tenth com- 

 missure, fig. I, 10, lies four sections posterior to that of the ninth; 

 it is present in four sections, and has a dorso-ventral measurement 

 of 42/x. The anterior surface of the commissure is a straight line, 

 the posterior, a curve, owing to the greater antero-posterior 

 dimension of the median part. The roots come from the fibrous 

 core of the brain lobes, and their fibers then run into and through 

 the oesophageal nerves, making a commissure that may be termed 

 hrain-cesophageal. The relation between the fibers of the roots 

 of commissures nine and ten will now be described. Leaving the 

 central part of the ninth commissure, the fibers run outward 

 beneath the oesophageal nerves and then slant upward toward 

 the brain lobes, making an oblique fiber band along the lateral 

 surface of each oesophageal nerve. In the following sections the 

 band becomes broader, and the more dorsal fibers, which are from 

 the roots of the tenth commissure, enter the oesophageal nerves 

 on their lateral, and pass out again from their medial surfaces to 

 form the central, oesophageal, part of the tenth commissure. 



