714 ^L^ AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



bulb, in which case the vessels supplying a great area are controlled by a small 

 group of cells. 



The difficulty of an anatomical explanation is increased by the fact l that 

 Ott enumerates in animals six heat-centres : 1. The cruciate, about the Rolandic 

 fissure ; 2. The Sylvian, at the junction of the supra- and post-Sylvian fis- 

 sures ; 3. The caudate nucleus ; 4. The tissues about the striatum ; 5. A point 

 between the striatum and the thalamus, near the median line ; 6. The anterior 

 mesial end of the thalamus. 



The only other division of the encephalon, the functions of which can prop- 

 erly be described apart, is the cerebellum. This portion is among vertebrates 

 almost as variable in its development as the mantle of the cerebral hemispheres, 

 and in many fish and mammals is asymmetrical in its gross structure. 



The recent work 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 does not cause permanently either paralysis or anaesthesia, but the imme- 

 diate effects of an extensive injury are a paresis and analgesia as well as anes- 

 thesia mainly in the hind legs, and in consequence 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 to 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 hemis- 

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

 existing symptoms are not intensified by the removal of the remaining half. 

 The permanent condition of the muscles after operation is expressed by an 

 atonia, or lack of tonus, in the resting muscles; an asthenia, or loss of strength, 

 which was measured by Luciani, and was most marked in the hind leg ; an 

 astasia, or a lack of steadiness in the muscles during action ; and finally an 

 ataxia, or a want of orderly sequence, in the contractions of a muscle- 

 group. The general expression of these symptoms is a twist of the trunk, 

 the concavity being toward the operated side, combined with a disorderly gait. 

 At the same time there is no demonstrable permanent disturbance of tactile 

 or muscular sensibility. 



Though the two halves of the cerebellum are united by strong commissural 

 fibres, the complete division of the organ in the middle line is followed by a 

 disturbance of the gait which is only transitory. Hence it is inferred that the 



1 Ott : loc. cit. 2 Archives Italiennes de Biologie, 1 891-92. xvi. 



3 Philosophical Transactions Royal Society, 1894. * Brain, 1893, vol. xvi. 



