272 AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



motor cortex of the monkey toward the thalamus are fibres of smaller calibre 

 than those destined for the pyramidal tract-. 



Moreover, the studies of Tschermak ' ou the termination of the tracts 

 which continue the dorsal columns of the spinal cord in the interbrain, show 

 an abundant connection of the fibres, especially with the ventral cell-groups 

 of the thalamus. The connection may be either an actual ending of the fibre 

 or a termination by means of collaterals. 



When these anatomical observations are considered in connection with the 

 differences in the reactions of the frog with and without, its thalami, it appears 

 that cell-groups which increase the responsiveness of the central system 

 must be located here. On the other hand, in the case of Goltz's dog without 

 its fore-brain, the thalami (interbrain) were so largely damaged that it hardly 

 seems possible that they could have been much utilized in the reactions which 

 were made by that animal. 



Human pathology throws little light on the functions of the thalami — 

 though lesion of it is often accompanied by loss of power to express the 

 emotions through the muscles of the face — a symptom to which attention has 

 been repeatedly drawn. 



The Cerebellum. — The only other division of the encephalon, the func- 

 tions of which can properly be described apart, is the cerebellum. This 

 portion is among vertebrates almost a> variable in its development as the 

 mantle of the cerebral hemispheres, and in many lish and mammals is asym- 

 metrical in its gross structure. 



Observation on this subdivision has been carried out in the first instance 

 by Luciani, 2 and later by Russell 3 and by Ferrier. 4 



The cerebellum is not concerned with psychical functions. The removal 

 of it docs not cause permanently either paralysis or anaesthesia, but the im- 

 mediate effects of an extensive injury are (in dogs and monkeys) a paresis 

 and analgesia as well as anaesthesia mainly in the hind-legs, and in conse- 

 quence a high degree of inco-ordination in locomotion. A distinct series of 

 symptoms, however, follows injury to this organ, and these are modified 

 according to the locality and nature of the lesion. Removal of one-half 

 (cerebellar hemisphere plus half the vermis) of the cerebellum in the dog 

 causes a deviation outward and downward of the optic bulb on the opposite 

 side, a proptosis of the bulbs on both sides, nystagmus and contracture of 

 the muscles of the neck on the side of the lesion, and an increase of the 

 tendon-reflexes in the limbs, in walking the dog wheels toward the side 

 Opposite lo the lesion, and tends to fall toward the side of the lesion. 



The symptoms are chiefly unilateral, and, caudad from the cerebellum, 

 are on the side of the lesion. The symptoms are less severe when only one 

 hemisphere, instead of an entire half of the cerebellum, has been removed. 



1 "Xutiz betreffi des Rindenfeldes der Hinteretrangsbahnen," XeurologischesCrninilblatt, 1898,, 

 No. 4. 



1 Archives italiennes df Biologic, 1891-92, xvi. 



1 Philosophical Transactions of the Royal Society, 1894. * Brain, 1893, vol. xvi. 



