THE SUBTHALAMIC REGION, ETC. 125 



nerve and of the opposite half of the body we may suspect 

 trouble under the corpora quadrigemina. Such patients have 

 either wholly or in part lost control of the limbs on one side of 

 the body, the upper lid droops, the pupil is dilated, and the 

 whole eye turned outward by the rectus externus. The same 

 symptoms might come from a tumor at the base of the brain, as 

 is evident from Fig. 57. It is, therefore, important for diagnostic 

 purposes to know whether the ocular paralysis appeared simul- 

 taneously with the paralysis of the extremities, a condition of 

 things which could only very rarely occur in the case of a tumor 

 at the basis cerebri. If anaesthesia appear, it is only present in 

 the side opposite the disease. The sensory fibres run to a great 

 extent in the lemniscus. 



If a disease-centre extend farther dorsad and involve the 

 corpora quadrigemina themselves, there appear, as may be easily 

 understood from a glance at our cross-section, paralyses of the 

 oculo-motor, which may involve either one or both nerves. In 



*/ 



disease of the anterior quadrigeminal body there is amaurosis ; 

 in some cases the ophthalmoscope reveals absolutely nothing. 

 In tumors, of course, as in tumors in other regions of the brain, 

 we may have choked disk, atrophy of the optic nerve, etc. 

 Generally, the pupil does not react either way. We do not 

 know what symptoms are caused by disease of the posterior 

 quadrigeminal body. Disturbances of equilibrium and co-ordi- 

 nation have been observed in such cases. 



We shall most strongly suspect disease of the corpora 

 quadrigemina if, in cases of paralysis of the oculo-motor, we 

 can exclude peripheral causes (on the base of the brain), or 

 when only a part of the oculo-motor (for instance, the fibres to 

 the internal muscles of the eye) is injured. In affections' of a 

 peripheral origin this would be impossible ; such paralyses are 

 nuclear. 



