646 TRANSACTIONS OF SECTION I. 
In our experiments six guinea-pigs were used. A lesion was made 
involving the whole of the motor cortex in the left cerebral hemisphere and 
the degeneration from it followed by the Marchi method. Above the decussa- 
tion nothing calling for special notice was observed except the relatively 
small area occupied by the transverse section of the pyramids in the medulla 
oblongata. Fibres begin to cross over from the degenerated pyramid about 
the level of the calamus scriptorius and continue to do so till the lower level 
of the medulla is reached. They are found in small but well-defined bundles, 
which after decussating pass backward through the grey matter, and then 
turn downward in the funiculus cuneatus, and, to a less extent, in the 
funiculus gracilis, close to the grey matter. In the first cervical segment 
they are found in the columns of Burdach and Goll, but a comparatively 
large proportion disappear in the grey matter of the bulb and probably end 
there. At the level of the seventh cervical segment they run down close to 
the postero-mesial border of the neck of the posterior horn and are much less 
numerous than in the first cervical segment. The number rapidly 
diminishes caudalwards and at the level of the fourth lumbar segment the 
tract is represented by not more than half a-dozen degenerated fibres. In the 
sacral region they are entirely absent. 
In the lower part of the decussation a very few fibres pass into the 
posterior column of the same side; these are not evident in the spinal cord 
below the second cervical segment. No fibres seem to pass into the lateral 
column of either side and none remain in the anterior column below the 
decussation. The proportion of crossed to direct fibres is much greater than 
in the cat, dog, or monkey. 
It is important to note that the relation of the fibres of the pyramid 
tract to the grey matter at the base of the posterior horn is the same in the 
guinea-pig as in those animals in which they run in the lateral column, the 
only difference being that in the one case they are placed on its postero- 
mesial and in the other on its antero-lateral aspect. Another point worthy 
of notice is the large proportion of fibres which, after crossing, terminate in 
the grey matter of the medulla oblongata, and the relatively small number 
which pass down the cord. 
5. Ascending Tracts in the Spinal Cord of the Cat. 
By E. G. Psrerson, A.B. 
The object of this investigation was primarily to ascertain whether there 
is any anatomical evidence for the statement that a certain proportion of 
the long ascending fibres of the posterior columns of the spinal cord from 
one side cross the middle line and pass up the corresponding column of the 
opposite side (Oddi and Rossi,’ Loewenthal,*? Van Valkenburg,* and others). 
The posterior roots were divided between the ganglia and the spinal cord 
on one side (right) in four cats. In one the fifth lumbar and seventh 
thoracic roots were cut simultaneously, in the second the fifth lumbar and 
twelfth thoracic, in the third the fifth lumbar alone, and in the fourth the 
eta cervical alone. The resulting degeneration was traced by the Marchi 
method. 
Where the double lesion was made the two zones of degeneration, with a 
clear area between, can be traced to the medulla oblongata where the fibres 
ef both zones end in the nucleus gracilis. No posterior column fibres are 
found at a higher level than these nuclei, and none are seen to join the 
* Oddi and Rossi, Arch. ital. de Biol. t. 13, 1890, p. 382. 
* Loewenthal, Internat. Monatsch. Bd. 10, 1893. 
* Van Valkenburg, Neurol. Centralb, 1909, S. 2. 
