STRUCTURE OF THE MESENCEPHALON. 



239 



arrived at the superior quadrigeminal body and formed the stratum 

 in question, they turn into the grey matter and end in arborisations. 

 The cells of the grey matter of this body are very various in form 



rtcx cerelri 



FIG. 270. DIAGRAM OF THE PROBABLE RELATIONS OF SOME OF THE NERVE-CELLS AND 

 FIBRES BELONGING TO THE RETINAL AND CENTRAL VISUAL APPARATUS. 



and size, and are disposed in several layers, which are better seen 

 in the optic lobe of the bird than in mammals. Most of their axis- 

 cylinder processes pass ventralward. Their destination is not certainly 

 known, but some appear to pass downwards with the fillet, whilst 

 others probably turn upwards and run in the tegmentum towards the 

 higher parts of the brain ; whilst others, perhaps most, probably form 

 terminal arborisations around the motor cells of the oculomotor of 



