1 86 Journal of Comparative Neurology. 



body, but the greater nurr^ber into the region immediately 

 behind it. 



The Optic Commissures. 



The two tracts of fibers forming the one the upper and the 

 other the lower optic commissure have already been described 

 in connection with the optic tracts. As noted there, I am un- 

 able to say definitely whether either give off branches to the 

 brain in passing, and it may be added here that I have no evi- 

 dence to show that a single nerve cell makes the entire con- 

 nection between the lobes, if such be actually the function of 

 the tracts. The question needs much further study. 



TJie Inferior Dorso -cerebral Conmiissures. 



The two groups of fibers connecting the lateral halves of 

 the dorso-cerebron immediately above the oesophageal fora- 

 men have been variously misunderstood. They are shown in 

 fig. lo where they appear as two short tracts in front of the 

 larger lower optic commissure. The anterior of the two was 

 supposed by the earlier writers to connect the antennal lobes, 

 and even the olfactory glomerulae of one side with those of the 

 other. Of such a direct connection I find no evidence what- 

 ever, though without doubt the two commissures may be con- 

 sidered as connecting the two deuto-cerebral lobes. In ordinary 

 preparations sectioned in the horizontal plane both commissures 

 are found immediately above the foramen, in fact almost bord- 

 ering upon it, and may be traced for a short distance into the 

 fibrillar substance of either side where the fibers curve slightly 

 downward and separating from the tract branch and disappear. 

 In frontal sections the fibers may be followed a little farther 

 than in those cut in a horizontal plane. In fig. 5 one of the 

 tracts may be seen though somewhat indistinctly. 



In bichromate of silver preparations, although I have fre- 

 quently found commissural fibers impregnated, I have not found 

 sufficient details to warrant a definite assertion as to the exact 

 relation of the tracts to the rest of the brain, nor as to the situ- 

 ation of the cells giving rise to their fibers. What details there 

 are, however, indicate that the anterior tract connects the two 



