The brain of Acipenser. 205 
the tectum and going via the decussatio transversa to the cortex in 
Ammocoetes. He also describes the bundle to the medulla. He 
does not mention a crossed portion of this bundle, nor does he 
mention a bundle to the lobi inferiores. 
HALLER (98) describes an anterior and posterior uncrossed tract 
to the lobus inferior, which are equivalent to the uncrossed tract in 
Acipenser. He also describes a crossed ’tween brain tract coming 
from the tectum, crossing above the chiasma, and ending in the median 
part of the ‘tween brain. I am in doubt whether this tract is pro- 
perly described. As figured by HALLER it bears a close resem- 
blance to the crossed tractus lobo-cerebellaris et bulbaris in Acipenser. 
3. Associational Fibres. 
The functions of association in the tectum are performed by cells 
whose neurites pass to the opposite side in the dorsal decussation. 
Such cells have been mentioned by CagAL (91), EDINGER (96b), and 
MAYER (97). Cells are present in the tectum of Acipenser whose 
neurites enter the dorsal decussation, but it is impossible to di- 
stinguish these cells in form and appearance from those whose neu- 
rites are destined to other parts of the brain. It is to be expected 
that there would be large provision for association in a center in 
which tracts from so many sources end. However, this function is 
probably served to a large extent by collateral fibres, which are more 
numerous, longer, and more richly branched in the tectum than 
in any other part of the brain of Acipenser. 
c) Commissura ansulata. 
The only attempt at a complete analysis of this commissure 
which has come under my notice is in EDINGER’s recent ‘tween 
brain paper (99). He divides all the bundles crossing in this region 
in Lacerta into four groups, beginning at the anterior: 
1. Bundles of the ventral part of the decussatio retroinfundi- 
bularis. 
2. a) A fornix component and fibres from the ganglion hypo- 
thalamicum. 
b) Slightly more caudal, fibres from the central grey. 
3. a) In. the midst of the out-going fibres of the III nerve, large 
decussations from the deep fibre layer of the tectum, in- 
cluding several kinds of fibres. 
