522 PHYSIOLOGY CHAP. 



on the basis of anatomical and clinical observations. Terrier (1878) 

 adopted this same point of view, partially on the strength of an 

 experiment on a monkey. After dividing the thalamns in this 

 animal by an incandescent wire introduced through the occipital 

 lobe, he noted among other less definite phenomena cutaneous 

 hemianaesthesia on the opposite side, blindness, and pupillar 

 dilatation, from which he concluded that the thalami are centres 

 in which the sensory paths converge and are interrupted before 

 radiating to the cortex. He remarked that if the thalami are the 

 relay centres for the sensory tracts, it follows that lesions of these 

 ganglia must produce an alteration in the various forms of 

 sensibility. This fact seems to be better demonstrated by the 

 study of clinical cases than by experiments on animals. Many ol 

 the cases described by Luys are not conclusive, since they are 

 tumours ; but certain cases of simple softening, confined more or 

 less clearly to the thalami, are very important from the physio- 

 logical point of view. 



Among the most valuable and best described clinical cases is 

 one of Hughlings-Jackson's (1875). The post-mortem examination 

 showed a considerable depression on the posterior half of the right 

 thalamus. On sectioning it was found to be softened and greyish- 

 yellow in colour. The softening did not extend beyond the limits 

 of the thalamus into the white matter of the hemisphere and 

 peduncle, and its anterior half and the posterior half of the corpus 

 striatum were intact. No other lesions could be found in the 

 brain. The symptoms obviously present in life with this well- 

 defined lesion of the optic thalamus were as follows : Weakness 

 of movements on the left side, especially in the leg, marked 

 diminution of tactile sensibility on the left, diminution of smell 

 or at least of ordinary sensibility of left nostril, slight diminution 

 of taste in left half of tongue, doubtful loss of hearing in left ear, 

 and finally, left hemiaiiopsia in both eyes, i.e. blindness of right 

 half of both retinae (bilateral homonymous hemianopsia). 



Experimental researches, when uncomplicated by lesions of 

 other parts, partially confirm the results of clinical observation. 



The prolonged researches of Lo Monaco (1898-1911) led to 

 the conclusion that of the effects of partial or total, unilateral or 

 bilateral extirpations of the thalami, the symptoms of visual 

 deficiency are the most prominent both from their gravity and 

 their persistence. 



Lesions limited to the internal or external part of one thalamus 

 produce very marked amblyopia of the eye on the opposite side, 

 while the eye of the side operated on shows no alteration to 

 ordinary tests. This amblyopia is not permanent, but gradually 

 disappears within a few weeks. No defect of the other special 

 senses can be observed, but there is a diminution of tactile and 

 painful sensibility on the skin of the opposite side. The circus 



