The brain of Acipenser. 219 
In describing the decussation itself he says that its fibres probably 
run from a ganglion on the dorsal outer side of the thalamus, 
crossing above and behind the chiasma, to the ganglion of the 
opposite side and to the ganglion isthmi. I presume that the fibres 
to the ganglion isthmi are the same as those described in the Vor- 
lesungen as perhaps going to that ganglion. These can not cor- 
respond to the bundle which in 1892 EDINGER traced with certainty 
to the tectum. The commissural fibres between the nuclei on the 
dorso-lateral surface of the thalamus in Reptiles are entirely new, so 
that there are three distinct tracts which EDINGER has referred to 
the decussatio transversa. The thalamus tract in Reptiles may cor- 
respond to that part of GUDDEN’s commissure which KÖLLIKER and 
others have traced to the corpus geniculatum mediale, thalamus, and 
nucleus lentiformis. A difficulty in the way of this interpretation is 
that EDINGER recognizes in addition to the nucleus of the decussatio 
transversa a doubtful geniculatum mediale, caudal to that nucleus. 
If we consider these together as equal to the geniculatum mediale 
in Mammals, EDINGER’s results on the decussatio transversa in Rep- 
tiles are in entire agreement with the descriptions of KOLLIKER and 
and others in Mammals. In this case we are without an explanation 
of EDINGER’s statement that the commissure of GUDDEN in Mammals 
runs to the posterior corpus quadrigeminum. 
The work of EDINGER & WALLENBERG (99a) on birds brings 
in new elements of complexity. The decussatio transversa is de- 
scribed as formed by fibres coming from the ganglion isthmi or from 
some source further caudally, which run parallel with the tractus 
isthmo-striatus and after crossing end in the ganglion entopedunculare, 
They describe also a decussatio inferior of MUNZER-WIENER dorsal 
to the chiasma. It is formed by fibres which end or arise in the 
nucleus lateralis. A bundle goes to the posterior quadrigeminum, 
and perhaps fibres go to the nucleus intercalatus, nucleus dorsalis 
anterior, and nucleus entopeduncuiaris. The bundle to the posterior 
quadrigeminum recalls EDINGER’s decussatio transversa of Selachians 
and Amphibians, and the ending of the other fibres in the nucleus 
lateralis and thalamus nuclei recalls the nucleus of the decussatio 
transversa of Reptiles and suggests homology with the GUDDEN’s 
commissure of Mammals (KOLLIKER and others). 
To sum up, in the work of EDINGER (including E. & W. on 
birds) fibres having their origin or ending in the following nuclei 
are described under the name of the decussatio transversa: 1) dorso- 
