THOMPSON YATES LABORATORIES REPORT 
V. Mesencephalic System of Fibres 
A system of efferent fibres from the mesencephalon to the cord was described in the Cat by- 
one of us* and by Held.! In the Cat it was shown that Forel's decussating fibres formed the 
efferent lateral columnar fibres, whilst anterior columnar fibres degenerated in the posterior 
longitudinal bundle. A similar system was shown by us to exist in the Bird at the Neurological 
Society's meeting (June, 1897), and this is also described in their recent paper by Munzer and 
Wiener. 
These observers distinguish, after lesion of the optic vesicle, as degenerating tracts, the 
(a) Tractus tecto-bulbaris profundus cruciatus — Forel's fountain decussation — which, 
crossing over the median line to a position ventral to the posterior longitudinal 
bundle, can be traced caudalwards into the medulla oblongata. 
(/3) Tractus tecto-bulbaris superficial'is non-cruciatuSy which passes ventrally, remaining 
superficial, and loses itself in a ganglionic mass, which corresponds to the 
trapezius nucleus of rabbits. 
They also succeeded in obtaining degeneration of the descending Vth root, 
(y) Tractus tecto-cerebellaris^ which passes from the ventral and posterior part of the 
optic lobe and ends in the cerebellum, partly in the nucleus of the ' Kleinhirn 
Korper,' partly in the ventral lobules of the middle of the cerebellum. 
Our own observations agree in the main with those of these writers, and the investigation 
of the origin and destination of these tracts shows the marked resemblance which exists between 
this system in Birds and Mammals. After injuries to the mesencephalon we find that there arise 
a system of arciform fibres which sweep across the formatio reticularis, and for the most part 
decussate in the middle line. The commencement of this system is shown in Fig. 28, Plate VII, 
where fibres can be seen streaming in from the mesencephalon to cross the raphe. This origin 
corresponds to that of the ' fountain decussation ' of Forel. In the series of transverse sections 
(Figs. 41-44, Plate IX) extending from the upper level of the origin of the Ilird nerve to the origin 
of the IVth nerve, the degeneration which these fibres undergo after lesion of the mesencephalon 
is well shown. They occupy especially two regions of the formato reticularis, (i) a deeper dorsal 
position, (2) a more superficial ventral position, and correspond respectively with the antero-lateral 
and lateral columnar fibres described by one of us, i.e.^ with the fountain decussation of Meynert 
and Forel. After their decussation they form a descending system of fibres, and are seen in all 
sections below this level, extending as far as the cervical region of the cord (Figs. 47-50, Plate IX)r 
In those cases in which the lesion was made at a lower level of the mesencephalon, and involved 
also the lateral region of the medulla, a third system of decussating fibres appears, which is situated 
dorsally and apparently supplies fibres to the posterior longitudinal bundles (Fig. 46, Plate IX). 
The degeneration of these fibres is very well marked (Fig. 47, Plate IX), and they probably 
in part go to form the ventral fibres of the cord (Fig. 50, Plate IX), being supplemented by those 
derived from the higher origin. 
* Boyce, ' Phil. Trans.,' B, 1895. 
t HeM, 'Arch. f. Anat. iind Phys.' 1892. 
