THE OPTIC LUJJtiS. 



151 



Fig. 104. 



duct, hence in a transverse section taken in front of this point 

 (Fig. 104 /') the cavity of either side appears to be isolated; in 

 a horizontal and longitudinal section (Fig. 105 Aq) the general 

 arrangement of the parts may be well seen. 



The grey matter 

 is chiefly arranged 

 in a layer so as to 

 surround the cavity 

 (Fig. 104), this layer 

 being deeper on 

 either side of the 

 descending portion 

 of the cavity than 

 elsewhere. For the 

 rest the grey matter 

 is much interspersed 

 among the white 

 matter, except at the 

 circumference of the 

 section, which is en- 

 tirely formed of white 

 matter. It contains 

 a large number of 

 small cells, of which 

 the nuclei are alone 



Visible ' 111 the parts Transverse section through the anterior portion of the optic lobes 

 opposite the origin of the motor-oculi nerve ; from Stieda (mag- 



mentioned where the nifled 3 o-8o). 



layer is most marked Lower portion of cavity. 



these cells are ar- h> ^^1^0 of cavity. 



M Ganglia of oeiih- motor nerve. 



Oculo-motor nerve. 



tc Large cells of the optic lobe. 



x Roof of optic lobe. 



y Posterior commissure. 



c Anterior divertieuluru of the cavitv. 



ranged in oblique 

 rows, between which 

 pass tine bundles of 

 medullated fibres 

 (Fig. 104, between u and //'). A group of large cells (Fig. 104 //) is 

 found on either side of the middle line and under the floor of the cavity ; 

 the cells are about 0-032 mm, long, and o - oi6 mm. broad ; the oculo- 

 motor nerve may be traced to this group, which is the oculomotor 

 nucleus. A small commissure of decussating fibres connects the 

 nuclei of opposite sides (Kijppen). 



The substance of the roof of the optic lobes (Fig. 104 a] is 

 arranged in verv distinct lovers : above is a laver free from cells ; 



