

—1905.] Thalamus and Deiter’s Nucleus to Spinal Cord, ete. 363 
about one-half of one lobe had been removed, and further removal had no 
other effect. Removal of one lateral half of the posterior part of the 
superior vermis caused an increase in the homolateral knee-jerks. 
In both cats and dogs injury to other parts of the mesencephalon, and 
simply scratching the superior cerebellar peduncle, caused the homolateral 
knee-jerks to become increased. 
The results of these experiments can be summed up as follows :— 
1. Decerebrate rigidity does not commence till the lesion passes through 
the posterior part of the thalamus and is independent of any injury to the 
pyramidal system. 
2. The inhibitory centre lies in the thalamus, the control is a crossed one, 
and the decussation takes place high up. 
3. The cerebellum has no influence on decerebrate rigidity; the adjuvant 
centre 1s Deiter’s nucleus. 
4. Decerebrate rigidity does not appear to be due to the interruption of 
the afferent channel of the cerebro-cerebellar circuit. 
5. The tonic condition depends upon the reflex arc being intact; injury to 
the posterior columns or the direct cerebellar tract has no effect. 
6. A condition of extensor rigidity occurs after partial or complete removal 
of the tentorium, bisection of the vermis, injury to the vermis, or partial cere- 
bellar ablation. 
The results as regards the knee-jerks agree with those obtained by Risien 
- Russell in dogs, and by Ferrier and Turner in cats and monkeys. Complete 
removal of one hemisphere, however, is not necessary to produce the changes. 
~B. The Results obtained by Stimulation of the Middle and Superior Cerebellar 
Peduneles, 
In order to expose the peduncles of the cerebellum the posterior part of 
the calvarium, the tentorium, and the greater part of the posterior fossa on 
one side were removed, the occipital lobe was drawn up, and the cerebellum 
drawn back to expose the middle peduncle. Stimulation of the middle 
peduncle produced bilateral, facial, and nasal movements most marked homo- 
laterally. The trapezii and pectorals of both sides were affected, the fore- 
limbs were protracted at the shoulder and flexed at the elbow, the hind-limbs 
were slightly flexed and drawn up. The back muscles were also thrown into 
a state of contraction, the effect in all parts being especially homolateral. 
Eye movements also occurred. They were, however, very various, usually 
movement towards the homolateral side. 
Stimulation of the superior peduncle was not very often successful; in the 
majority of cases the results were the same as for the stimulation of the 
2B 2 
