Herrick, Central Atrophy After Eye Inpnics. 3 



same number of fibres in the root of the fourth nerve on either 

 side. (See Fig. 4.) The external portion of the fourth nerve 

 of the right side is apparently wholly degenerate while its fel- 

 low of the opposite side is intact. For some reason, then, the 

 degenerative process has destroyed the central tract and nidulus 

 of the third nerve but not those of the fourth, though the ex- 

 ternal part of the latter has disappeared. We find no central 

 tracts degenerate between the fourth and sixth nerve niduli, but 

 the latter has as completely disappeared as in the case of the 

 oculo-motor. Nothing is left of root, tract or nidulus. The nid- 

 ulus of the left side lies, as usual, just laterad of the genu of 

 VII and its root tract turns sharply mesad beneath the VII 

 fibres and then passes directly ventrad to the root. Some traces 

 of the sheath may be found by careful search in the course of 

 the root of the other side. 



The result of the operation, then, has been as follows: (i) 

 degeneration of the lateral three fourths to five sixths of the 

 left optic tract and of the mesal one fourth to one sixth of the 

 right tract, (2) proportional atrophy of the optic tecta, most 

 marked on the left side, (3) obliteration of the nidulus, root 

 tracts and roots of III and of the external part and roots of IV 

 on the right side, (4) the obliteration of VI on the left side as 

 completely as III. Negatively, the central portions of IV are 

 unaltered and the interpeduncular niduli are intact. 



The rabbit of series 297 was operated on earlier and the 

 results are rather of the nature of atrophies than of degenera- 

 tions. The diameter of the left optic nerve is somewhat more 

 than one fourth that of the right. At the chiasm, as seen in 

 Fig. 7, the proportions are about the same. The degenerated 

 portions are almost completely absorbed leaving only atrophic 

 phenomena. Sections further caudad show very distinctly the 

 atrophy in the tract. (Fig. 8.) 



At the proper level the corpus geniculatum of the left side 

 appears with its tracts, but on the other side it seems quite ab- 

 sent. There are no degenerative changes to enable us to trace 

 the tracts cephalad to the cortex but there seems no reason to 

 doubt that they are atrophic throughout. The reduction in the 



