130 J. B. JOHNSTON, 
98a). I have since convinced myself that the fibres crossing here 
pierce the fasciculus from other sources. I have described the 
relation of the fasciculus to the motor nerves of the medulla. I can not 
tell whether any fibres of the IV nerve arise from the fasciculus. 
A part of the fibres of the III nerve appear in haematoxylin sections 
to come from it. 
4) Tractus sacco-thalamicus. — 
5) Tractus thalamo-saccus. — These tracts have been 
fully described above (page 119 ff.). 
The tracts entering the thalamus from the fore brain I shall 
describe in connection with that part of the brain. 
c) Tracts of the Epithalamus. 
1) The disposition of the tracts entering the ganglia habenulae 
from the epiphysis and from the olfactory area of the fore brain 
has been described above (page 110). I have also described an epi- 
physial decussation and the course of the fibres composing it, as 
far as I have made them out (page 108). 
2) Bundles of MEYNERT. — The manner of origin of these 
bundles has been described (page 110) and I have noted the larger 
size of the right bundle and the larger number of fine fibres in it. 
The two bundles run caudo-ventrad near the central cavity, but 
separated from it by occasional cells and fibres. They reach the 
base of the mid brain at about the point at which it bends down 
into the corpus mammillare. There they turn caudad in a super- 
ficial position near the ventral raphe. From this point on, the 
coarser and finer fibres have a different disposition. The fine fibres 
remain in an extreme ventral position and some of them decussate 
at an acute angle beneath the cephalic part of the commissura an- 
sulata, while others diverge to right and left without decussating. 
Both crossed and uncrossed fibres pass into the medulla and probably 
run caudo-dorsally around the lateral surface of the medulla to end 
in the granular layer of the lateral lobes of the cerebellum. The 
coarse fibres turn slightly dorsad and pierce the cephalic part of the 
ansulate commissure. Beneath the caudal part of the commissure 
they decussate at right angles and at the same time give off numerous 
collaterals. After decussating the fibres turn abruptly dorsad, at 
either side of the ventral raphe and groove, pass around the ental 
surface of the fasciculus longitudinalis posterior, and end among the 
