306 LEIGH HOADLEY. 



sections of the lobe, in which fiber tracts appear, running for some 

 distance across the field. Longer fiber tracts appear in the inner 

 fiber layer. These run into the base of the lobes, through which 

 all of the innervation of this region finds its exit. The basal por- 



v.s. 





Mesoc. 



FIG. 9. Cross section of a portion of the tectal part of the mesencephalon of a 

 chick of eight days incubation. (X 180.) E.L.M., external limiting membrane. 

 Ep.N.L., epenclymal nuclear layer. I.F.L., inner fiber layer. Mesoc., mesocoele. 

 M.N., nuclear strands. O.F.L., outer fiber layer. O.N.L., outer nuclear layer. 

 V.S., vascular sheath in the mesenchyme. 



tion also contains fibers of the ascending and descending nerve 

 tracts. No peripheral nerves are present. The vascularization 

 of the region is accomplished by small vessels which enter the 

 nervous tissue through the external limiting membrane. 



Bearing this general condition in mind, an examination of the 

 sections of graft 38 A 4 shows, with a few exceptions, a genc-r.il 

 conformability of its development to that of the normal. The 

 two greater cavities of the control are represented by one large 

 mesocoele. This is bounded by the basal and tectal portions of 

 the grafted tissues. The basal portion gives a rather compart 

 appearance with many fiber tracts. In the cortical n-gion tin- 



