ix MID- AND INTEE-BKAIN 517 



lesions (if these bodies motor disturbances in the eye were either 

 totally absent or appeared only when the lesion was so extensive 

 as to involve the grey matter that surrounds the Sylvian aqueduct. 

 Hesen and Volkers and Bechterew came to the same, conclusion. 

 This contradicts the views of Terrier and of Adamiik, who con- 

 cluded from the excitation method that the anterior 1 todies con- 

 tained special centres for the conjugate movements of the eyes. 



(e) Nor do the quadrigemina contain the centre for the move- 

 ments of the iris, disturbance of the latter being only seen when 

 the lesion extends to the oculo-motor nucleus, i.e. when it involves 

 the grey matter that surrounds the aqueduct of Sylvius. Lussana 

 and Lemoigne and Bechterew also assumed that the centre for 

 the iris was not situated in the corpora quadrigemina, but lay 

 deeper. 



(/') Circus movements, paresis or paralysis of the limbs, and 

 disturbances of equilibrium appear as transitory phenomena when 

 the lesion is limited to the corpora quadrigemina. They must 

 therefore depend on the excitation or destruction of the subjacent 

 or surrounding parts. Circus movements which are usually 

 towards the side of the lesion are due to the hemiparesis, and 

 disappear as the latter wears off; the movements towards the 

 opposite side depend on the excitation of the, subjacent pyramidal 

 fibres and are quite transient. 



Sgobbo follows up his series of experiments on dogs by a critical 

 review of the clinical cases described by various authors in which 

 post-mortem examination showed lesions limited to one or other or 

 both of the corpora quadrigemina, with a view of ascertaining the 

 functions of these ganglia in man. 



After minutely analysing the complex symptomatology of these 

 cases, he came to the general conclusion that both isolated lesions 

 of the anterior and posterior corpora quadrigemina and lesions 

 involving both these bodies failed to produce any constantly 

 appreciable alteration in vision or hearing. It is possible that in 

 proportion as the prosencephalon acquires a greater importance in 

 the zoological scale the functional importance of the mesencephalon 

 in general, and of the quadrigemina in particular, may diminish. 

 For the better solution of this question it is desirable that a 

 methodical series of experiments should be carried out upon the 

 corpora quadrigemina of monkeys, which come nearest to man in 

 the relative development of these segments of the brain. 



IX. The function of the centres of grey matter which lie deep 

 in the mid-brain and cerebral peduncles is very obscure and un- 

 certain. It is only known that lesions of the mesencephalon 

 produce forced movements as their immediate consequence. 

 Sherrington (1896) described some important effects of sections of 

 various extent, at the level of the mid-brain. In the monkey he 

 contirmed the fact that section in front of the mid-brain leaves 



