204 J. B. JOHNSTON, 
in the decussatio transversa (commissura inferior GUDDEN), to the 
nucleus anterior (?), and perhaps to the fore brain. 
AUERBACH (’87) describes tracts which go to the reticular 
formation of the base of the mid brain, to the commissura inferior 
GUDDEN, to the anterior decussation of the regio subthalamica, and 
to the torus semicircularis. 
EDINGER describes the cerebellar and bulbar tracts in the Vor- 
lesungen (96b) and in his first paper on the ‘tween brain (92) says 
that the decussatio transversa in Selachians and Amphibians (MEy- 
NERT’s commissure in Mammals) is composed of fibres from the 
tectum. In his second paper (99) he states that the fibres of the 
decussatio transversa probably come from a ganglion on the dorsal 
outer side of the thalamus in Reptiles and cross to the ganglion of | 
the opposite side and to the ganglion isthmi. EDINGER WALLEN- 
BERG (99a) describe this decussation in birds as formed by a bundle 
coming from the ganglion isthmi or from some more caudal source, 
which after crossing ends in the corpus ento-pedunculare. These 
are perhaps the same bundle and nucleus as described in the Reptilian 
brain (EDINGER, 99). It is clear, however, that this bundle has no 
relation to the bundle forming the decussatio transversa in Selachians 
and Amphibians. This bundle EDINGER finds arising in the tectum, 
but he does not give its destination. In Acipenser I find only one 
tract in this position and it forms only a very small part of the 
decussation behind the chiasma (cf. page 220 below). Only the most 
anterior part of this decussation is formed of fibres coming from 
the tectum, and these follow close along the border of the optic 
tract. It has been impossible for me to follow the bundle with 
certainty after crossing. I have been in doubt whether to call it a 
part of the tractus tecto-lobaris cruciatus, or a tract to the fore brain. 
Since EpINGER describes only a part of the decussation behind the 
chiasma it is difficult or impossible to identify his tracts. In Aci- 
penser there is probably one tract between the tectum and fore brain. 
Whether there is a second in lower Vertebrates I am in doubt. 
EDINGER says that the tract which he calls Mantelbiindel may not 
have the same origin in Amphibians as in Selachians, but he traces 
it into the tectum in both. This can not be decided until the ex- 
tremely complicated decussations behind the chiasma are unravelled 
and especially until the tracts which EDINGER overlooked are de- 
scribed in Selachians and Amphibians. 
MAYER (97) mentions fibres arising from the bipolar cells in 
