349 



Now i( is interesting to note, tliat in tliis latter period fresli 

 additions to our knowledge of the physiological function of this 

 important structure (P. J^. B. formation) came from quite other (juarters, 

 viz. from clinical anatomy. As 1 wish to I'eserve a detailed 

 account of these data for another occasioJi, I will confine myself to 

 stating, that the wellknown symptom of conjugated deviation — being 

 a subphenomenon of the symptom of circus movement — appeared to 

 stand in a direct relation to a lesion of the P. L. B. in such a way 

 that destruction of the right P. L. B. caused conjugated deviation to 

 the left. As we saw in a former publication ^), hy purely physiolo- 

 logical and anatomical methods practically the same conclusion was 

 arrived at for circus-movement in the cat. It cannot be denied, 

 that both lines of thought complete each other very nicely. The old 

 law of Schiff-Probst ("A hemisection of the jions causes circus move- 

 ment to the normal side ; of the mesencephalon to the affected side") 

 had, so it appeared, to be read in this way: a section of aP.L. B. 

 results in circus movements to the non-sectioned side ; a lesion of the 

 posterior commissure results in circus-movements to the affected side". 



The further physiological analysis of the lateral wings of the 

 P. L. B. formation . in cats, as we have attempted in this paper, 

 discloses at all events the important fact, that this part of that 

 structure holds fibres of equally vestibulary origin, but of different 

 function. The degeneration of these tracts brought about either by 

 direct lesion or by a lesion of its nutrient grey matter, results in 

 forced movements in another plane, viz. rolling-movements, and the 

 allied conjugated deviation, the Magenpie-Hertwig squint. Here the 

 relation between the ascending and descending tracts, controlling 

 these movements, became not ^o transparent, as was the case with 

 those controlling the circus-movement. 



F'or the latter we found, that the gray matter near the posterior 

 commissure was at the same time the endstation of the ascending 

 tracts and the origin of the descending tract. For the rolling-move- 

 ments it was proved, that the ascending bundles terminate in the 

 tegmentum near the IV Nucleus, whereas we could only hesitatingly 

 indicate one or two paths, tiiat might be considered as the corre- 

 sponding efferent tract. In another publication I intend to deal with 

 those ascending vestibulary connections, whose lesion causes forced 

 movements in a third plane (the vertical plane, that coincides with 

 the long axis of the body) viz. staggering and culbutation. Proof 

 will be forthcoming, that they run iji entirely different structures 

 as those, dealt with in this and ihe former papers. 



i) Transactions Royal Dutch Academy. 25 Oct. 191i2 and Neuraxe 1913. 



