i84 THOMPSON YATES LABORATORIES REPORT 
1. Gudden's Commissure or Commissura Inferior (Bellonci). — This commissure is seen in 
the horizontal sections (figs. 13 and 14, Plate V), and in sagittal sections (figs. 16 and 17, Plate VI). 
In the former plane it appears as a distinct band of fibres immediately behind the optic chiasma, 
internal to the deep branch of that tract. In fig. 15, Plate VI, it is cut in transverse section and 
appears to give fibres to the optic chiasma. 
Fig. 13 shows that it has an origin in the grey matter of the interior of the optic vesicle, 
and in sagittal sections (figs. 16 and 17, Plate VI) fibres are seen coming down from the nuclei of 
the thalamus. 
In fig. 15, Plate VI, where it is cut in transverse section, it appears to give fibres to the 
optic chiasma. 
2. Commissura Post-Chiastnatica (described by Edinger in the Reptiles). — This commissure 
is well seen in Fig. 14, Plate V, and consists of a well-marked band of fibres which sweeps round 
the ventricle anteriorly, closely applied to the optic chiasma, and to which it appears to give fibres 
(Fig. 15, C.p.c). It is immediately posterior to Gudden's commissure. Its fibres pass backwards 
on each side (Fig. 14, Plate V) in a horizontal plane to the ganglion ectomammillare, or nucleus 
peduncularis (Bellonci). It will be observed that this tract in horizontal sections makes a 
considerable angle with Gudden's tract, the latter is much more external than the former. 
Bellonci figures a tract having a very similar position to this, and describes it under the name of 
the Dccussatio Inferior. As this writer suggests, it is probably the representative of the Fibras 
Ansulatas of other types, a decussating system existing in the Reptiles and Amphibians, and 
regarded by Bellonci as corresponding to Meynert's commissure in Mammals. 
Their termination in the ganglion ectomammillare is well seen in our figures ; whether 
they pass after decussating to the upper part of the thalamus, as stated by Bellonci, is uncertain. 
3. Commissura Supra Infundibularis. — This commissure is also well seen in Fig. 14, 
Plate V, having an opposite position to the previous commissure, and decussating behind the third 
ventricle. Its fibres appear to arise in the lateral walls of this ventricle. 
4. Epithalamic Connection. — In sagittal sections (Figs. 17 and 18, Plate VI) a scattered band 
of fibres are seen to come down from the roof of the thalamus, perhaps from the ganglion 
habendulae, and to pass forward, behind the anterior commissure, to a position in front of the 
optic chiasma, to which place also fibres from the pallial tracts converge, as described in the next 
paragraph. 
5. Pallial Connection. — The middle group of pallial fibres, which pass backwards in front 
of the anterior commissure to a spot immediately in front of the chiasma, have already been 
described, and are seen in Figs. 16 and 17, Plate VI. 
6. Connection with the Ganglion Isthmi. — This tract, which will be described later on, is a 
well-marked tract which, after lesion of the medulla in the region of the ganglion isthmi, undergoes 
degeneration, and can be traced into the optic tract (Figs. 40-45, Plate IX). 
7. Connection with the Hemispheres and Thalamus. — Bellonci describes bands ot fibres 
passing from the region of the ganglion ectomammillare and the interior of the optic lobes to end 
respectively in the fore brain and in the thalamus. Our sections do not afford sufficient evidence 
