138 J. B. JOHNSTON, 
portion of the ansulate commissure (Fig. M, A) consists entirely of 
fibres of this sort. They surround and are interwoven with the 
rootlets of the III nerve. They are medium-sized medullated fibres 
whose sheaths do not blacken so readily with osmium as do those of 
other parts of the commissure, so that in sagittal sections this part 
of the commissure is clearly distinguished by its lighter color. 
2) Tractus tecto-lobaris cruciatus. Forms the superficial or 
ventral part of the commissure at its cephalic end. 
3) Tractus tecto-bulbaris cruciatus. Lies immediately behind (2). 
4) Tractus bulbo-tectalis. Forms the dorsal or deep part of the 
commissure at its cephalic end. With this is a bundle which has 
its origin in the torus semicircularis Halleri, a part of the crossed 
tractus tecto-bulbaris. 
5) Fibres of the end-nucleus of the bundles of MEYNERT. These 
run singly in the middle and caudal part of the commissure. 
6) Arcuate fibres from the acusticum. 
7) Fibres from the Acusticuszellen of GORONOWITSCH. 
8) Decussation of MEYNERT’s bundles. 
g) Decussations in the Hypothalamus. 
1) Decussatio praemammillaris (Decussatio suprainfundi- 
bularis EDINGER ?). In the cephalic and dorsal wall of the corpus 
mammillare is a decussation of considerable size, the fibres of which 
I have been unable to trace satisfactorily to their source and de- 
stination. They seem to arise from cells of the central grey near 
its junction with the lobi inferiores and, after decussating, to turn 
forward in the tractus strio-thalamicus to go to the fore brain. 
2) Decussatio postoptica. It is extremely difficult to 
make out all the fibres in this decussation but I believe that it is 
made up wholly of the crossed tractus lobo-bulbaris, tractus tecto- 
lobaris, and the tractus strio-tectalis. 
h) Decussation in the dorsal Wall of mid and ‘tween 
Brain. 
1) The dorsal decussation in the tectum belongs to the middle 
fibre zone. It may contain commissural fibres from one half of the 
tectum to the other, but I know no evidence that its fibres do not 
all join the tracts to the lobi and the medulla. 
2) Commissura posterior. — In frontal sections the 
fibres of this commissure spread through the lateral walls of the 
