pS Journal of Comparative Neurology. 



and the collection of the fibres of the cephalic optic brachium 

 begin to gather over the region of the geniculatum. A nidulus 

 of large cells accumulates near the aqueduct caudad of the hab- 

 ena ; this we may call nidubis aqucdiicti. 



6. Proceeding still ventrad, a point is reached where the 

 few fibres of the t^nia thalami enter the median wall of the hem- 

 isphere from the cephalic base of the habena. These fibres are 

 so few as to easily escape notice. 



7. At the point where the cerebellum becomes attached 

 to the corpora posterior, a strong decussating band comes into 

 view immediately caudo-dorsad of the decussation of the troch- 

 learis (Fig. 3, mid. p., Plate VII — Fig. i (9), Plate VI — Fig. 

 6, mid. p., Plate X.) These fibres, which are derived, via the 

 corpora posterior, from bundles ascending from the pes peduncu- 

 li, decussate and pass into the ventricular layer of the cerebellum. 

 The whole interior of the "colliculi" (Riickhard) or projection 

 into the optic ventricles now become filled with isolated bundles 

 of the sensory system. 



8. Somewhat ventrad of the decussation of the middle 

 peduncles of the cerebellum just described there appears a small 

 dense nidulus caudad of the geniculatum and laterad of Mey- 

 nert's bundles (thus somewhat cephalo-laterad of the tracts from 

 the post-commissure.) This seems to be the homologue of the 

 corpus rotundus of fishes or, according to our definition, the 

 nidulus ruber. Like the corresponding organ in fishes it con- 

 tains fibres passing toward the post-commissural region. 



Fibres from the caudal brachium begin to collect caudad of 

 the optic tract and assume the well known relations of this ele- 

 ment of the inferior commissural system. In the region of the 

 praecommissure the fornix fibres collect just as in fishes and de- 

 scend toward the tuber. 



9. The nidulus of the trochlearis appears below the site 

 of the scattered cells of the mesencephalic nidulus of the trige- 

 minus, and gradually receives its tract, which remains medullated 

 and very distinct. The tract from the post-commissure seems 

 to merge insensibly into the dorsal longitudinal fasciculus ven- 



