89 

 scribed from the optic lobes of biris, but it is pricticable 

 to jistiaguish three zones of structural elements: the layers 

 of the superficial, the millLe, and the deeper neurones, res- 

 pectively, (Pig.?l,3.n. ,m. n. ,d. n. ). VanGehuchten ('94) has 

 described three zones frona the optic lobe of the teleost, but 

 these are not exactly equivalent to the layers noted here, 

 his conohe moleanlaire appears to include both my superficial 

 and middle layers; his couohe granul ease corresponds in posi- 

 tion to any deeper layer; /vhile his ooaohe ies oell-iles eoeniy- 

 maires is an inner zone .vhich apparently does not include the 

 central gray matter. 



a. TerTiiiation. of the Opticus. S tr . '.feiul I are Pro fund um. — A 

 great bundle of fibres may be traced dorso-posteriorly from each 

 angle of the chiasma to the optic lobe, flhere it becomes dis- 

 solved through spreading over the surface. A section sho-vs 

 that the fibres in the outer zone lie parallel with the sur- 

 face during some little part of the length of their course, and 

 that they then pass do.vn/iard into deeper parts of the tectum. 

 Fine branches are given off in the regions occupied by the 

 neurones of the middle and deeper layers, and many terminations 

 appear to occup here. A certain number of fibres, however, 

 pass to ever deeper levels, tending to become collected into 

 bunlles, and they finally blend into tne stratum medullare 

 prof undum. 



The stratum meiullare profundum is a conspicuous feature 



