The brain of Acipenser. 145 
fibres from the cells of the nucleus taeniae, pierce the optic bundles 
in the chiasma and bend down into the hypothalamus. They have 
their endings in the lobi inferiores. This bundle also contains as- 
cending fibres (see below). The lateral bundle contains fibres from 
the nucleus postolfactorius lateralis and from the striatum. It runs 
near the lateral surface of the fore brain, pierces the mesial part 
of the optic tract dorsal to the chiasma, enters the thalamus just 
lateral to the median bundle and is distributed to the dorsal and 
lateral wall of the inferior lobe. In Pl. 13 the lateral bundle is in- 
corporated with the median. The median bundle is much the largest 
and contains the greater part of the descending fibres from the 
striatum and of the ascending fibres to the epistriatum. The de- 
scending fibres enter the thalamns mesial to the optic tracts and are 
distributed to the central grey of the thalamus and to the dorsal 
wall of the inferior lobe. There is some evidence that a part of 
its fibres reach the corpus mammillare. 
The ascending fibres to the fore brain arise chiefly in the corpus 
mammillare. A part arise from the ventral wall of the corpus 
mammillare and run forward along the ventral face of the inferior 
lobe, to enter the fore brain as a part of the ventral bundle of the 
tractus strio-thalamicus. The greater part of the ascending fibres 
arise from the dorsal and lateral walls of the mammillare (and from 
the ectomammillare?) and pass forward in the median bundle. Most 
of the ascending fibres cross to the opposite side in the anterior 
commissure, but apparently some find endings in the epistriatum of 
the same side. 
2) Tractus olfacto-habenularis. — A certain number of fibres 
from all the olfactory centers (see above and cf. page 235) take 
a dorso-caudal course through the striatum and epistriatum and col- 
lect into a compact bundle at the dorso-caudal angle of the fore 
brain, to run up into the ganglion habenulae. I have described fully 
the disposition of the fibres in the ganglia and the commissura 
habenularis (page 110). 
In describing the mid and the ‘tween brain I have mentioned 
two small tracts which probably connect some part of the fore brain 
with the tectum (cf. page 114, 128). 
F. Olfactory Lobes. 
In either haematoxylin or GOLGI sections in any plane three 
chief zones are readily recognized. Externally is a zone of olfactory 
Zool. Jahrb. XV. Abth. f. Morph. 10 
