220 J. B. JOHNSTON, 
caudal part of mid brain (Selachians); 2) caudal part of tectum 
(Selachians and Amphibians) or posterior quadrigeminum (birds and 
Mammals); 3) ganglion isthmi (Reptiles); 4) ganglion isthmi or some 
source further caudally (birds); 5) nucleus on the dorso-lateral sur- 
face of the thalamus (Reptiles). With these are probably to be in- 
cluded the fibres described in birds under the name of decussatio 
inferior, to 6) nucleus lateralis, other thalamus nuclei, and the 
posterior quadrigeminum. 
The decussatio postoptica is described by EDINGER only in 
Selachians and Amphibians. It is a decussation of his Mantelbündel 
ventral to the decussatio transversa, the fibres going to the tectum. 
He homologizes it with the decussatio transversa Halleri in Teleosts 
and with the commissure of GUDDEN in Mammals. 
The decussatio postchiasmatica which EDINGER mentions in the 
Vorlesungen (5th ed., p. 134) has been shown by EDINGER & 
WALLENBERG to be a part of the opticus in birds. 
FRIEDRICH MAYER (97) states that in Petromyzon the fibres of 
the commissura transversa belong to the Stabkranz, coming from 
the medulla and tectum. 
HALLER (98) describes the postoptic decussation in Seylliwm and 
Salmo as made up of two parts, an inferior including what he calls 
the Mantelbündel (= part of the tractus strio-thalamicus ?) and fibres 
from the nucleus rotundus; and a superior consisting of fibres from 
the tectum, mostly crossed, to the ventral ‘tween brain nucleus. This 
he calls Epınger’s Mantelbündel. He describes also a ‘tween brain 
tract from the tectum crossing above the chiasma. This description 
does not agree in any particular with the description of any other 
author. 
In my description of the “tween brain tracts in Acipenser 
(page 129 ff.) I have shown that the postoptic decussations are com- 
posed of fibres of the tractus lobo-cerebellaris et bulbaris, tractus 
tecto-lobaris, and perhaps the tractus strio-tectalis. The fibres of 
the last named tract constitute less than one-twentieth part of the 
whole decussation. Granted that they constitute a bundle connecting 
the fore brain and tectum, it must correspond to EDINGER’s Mantel- 
bündel and to his decussatio postoptica in Selachians and Amphibians. 
It is so closely applied to the other bundles that it can not be de- 
signated a separate decussation. The tractus tecto-lobaris makes up 
perhaps one-fifth of the whole decussation in Acipenser. This cor- 
responds to EDINGER’S decussatio transversa in Selachians and Am- 
