TRANSACTIONS OF SECTION I. 645 
3. The Pyramid Decussation in the Sheep. 
By J. Lus.ua Kina, A.B., and Surueruanp Simpson, M.D., D.Sc. 
Very little is known with regard to the course of the pyramid tract fibres 
in the ungulata. Ziehen,’ by differential staining with urancarmine and 
nigrosine, in an uninterrupted series of sections through the bulbar 
decussation in the sheep, believes that the pyramid fibres after crossing divide 
themselves into two groups; one passes to the recticular formation in the 
posterior part of the lateral column, the other goes through the grey matter 
and turns downwards in the lateral part of the column of Burdach. The 
posterior horn lies between the two divisions. Kingsbury (from unpublished 
work) with Weigert staining in the normal sheep, followed the decussated 
fibres, or many of them, into the posterior column. The results obtained by 
‘these methods, however, are not conclusive in tract tracing, since there is no 
means of knowing the source of the fibres under consideration. Only the 
developmental or degeneration method is of service. 
We have used six adult sheep and two young lambs, but the latter have 
not yet beenexamined. After first locating the motor area, which we found 
to lie in the superior frontal convolution, we extirpated it in the left cerebral 
hemisphere and followed the resulting degeneration by the Marchi method. 
The sections above the medulla oblongata have not been carefully examined 
as yet, and we deal here simply with the decussation. 
The degenerated fibres of the pyramid are finer than those in the cat, 
dog, or monkey. They pass backwards in the raphe toward the central canal, 
and then, turning abruptly outwards, direct their course through the grey 
matter to the recticular formation on the antero-lateral aspect of the 
posterior horn, in the bundles of which they appear to turn downwards. 
No degenerated fibres can be followed into the funiculus gracilis or funiculus 
cuneatus in the bulb nor into the columns of Goll or Burdach at a lower 
level. A large proportion of the fibres—in some sections almost an equal 
number—instead of crossing the middle line, turn outwards on the same side, 
and follow a course similar to that described for the crossed fibres. The 
posterior longitudinal bundles at this level in transverse section show a 
considerable number of black dots, but whether these represent degenerated 
fibres from the pyramid tract is uncertain. Below the first cervical segment 
of the spinal cord we find no evidence of any tract degeneration. The crossed 
and uncrossed fibres appear to end in the processus reticularis ; at all events, 
we have not succeeded in tracing them beyond this. 
The points of interest are—(1) that no pyramid tract, 7.e., cortico-spinal, 
fibres can be followed into the posterior columns ; (2) the large proportion 
of direct to crossed fibres ; (3) the fact that the fibres cannot be traced in 
the spinal cord below the first cervical segment. 
4. The Cortico-Spinal Tract in the Guinea-pig. 
By Ipa Z. Revewzy, M.A., and SutHervanp Smpson, M.D., D.Sc. 
The position of the. cortico-spinal or pyramid tract shows greater varia- 
tion than that of any other strand of fibres in the spinal cord. In the 
majority of mammals that have been investigated (man, monkey, cat, dog, 
rabbit) its main division—the crossed pyramid tract—lies in the posterior 
part of the lateral column, but in others—guinea-pig, rat, squirrel—it is 
said to run in the posterior column. The evidence for this statement is, 
in many cases, not conclusive, since the course of the fibres has been traced 
not by the developmental or degeneration method, but simply by following 
them in serial section through the decussation in the medulla oblongata down 
into the upper part of the spinal cord. 
1 Ziehen, Anat. Anz. Bd. 17, 1900, S. 237. 
