FUNCTIONS OF THE BRAIN 941 



hinder edge of the posterior corpora quadrigemina and the labyrinth, 

 being supported partly through spinal centres and partly through 

 pre-spinal centres mainly in the region of the pons, but partly in the 

 bulb (Sherrington) . But it is none the less true that the act of standing 

 is aided and regulated in important ways by centres in the mid-brain 

 and cerebellum through afferent impulses originating in the labyrinth 

 and elsewhere e.g., in the muscles. 



Ewald has made an observation which illustrates the peculiar 

 relation of the semicircular canals to the muscular system namely, 

 that the labyrinth (in rabbits), influences the course of rigor mortis 

 in the striped muscles. Rigor does not come on so soon on the side 

 from which the labyrinth has been removed. 



(2) Afferent Impressions from the Muscles. Muscles are richly 

 supplied with afferent fibres, for about half of the fibres in the nerves 

 of skeletal muscles degenerate after section of the posterior roots 

 beyond the ganglia (Sherrington). Various kinds of impressions 

 may pass up these nerves : (a) Impressions giving rise to pain, as in 

 muscular cramp and in experimental excitation of even the finest 

 muscular nerve-filament; (b) impulses causing a rise of blood-pres- 

 sure; (c) impulses which are not associated with a distinct impres- 

 sion in consciousness, but which enable us to localize the position 

 of the limbs, head, eyes, and other parts of the body; (d) impulses 

 which inform us as to the extent and force of muscular contraction, 

 and seem to underlie the so-called muscular sense. It is the last 

 two kinds if, indeed, they are distinct which must be concerned 

 in equilibration. In locomotor ataxia such impressions are blocked 

 by degeneration in a part of the afferent path (p. 915), and disorders 

 of equilibrium are the result. 



(3) Afferent Impressions from the Skin. Of the various kinds of 

 impulses that arise in the nerve-endings of the skin, only those of 

 touch and pressure seem to be concerned in the maintenance of 

 equilibrium. When the soles of the feet are rendered insensitive by 

 local anaesthesia or by cold, and the person is directed to close his 

 eyes, he staggers and sways from side to side. The disturbance of 

 equilibrium in locomotor ataxia must be partly attributed to the 

 loss of these tactile sensations, for numbness of the feet is a frequent 

 symptom, and the patient asserts that he does not feel the ground. 

 An interesting illustration of the importance of afferent impulses 

 from the skin in the maintenance of equilibrium is afforded by the 

 behaviour of a frog deprived of its cerebral hemispheres. Such a 

 frog will balance itself on the edge of a board like a normal animal, 

 but if the skin be removed from the hind-legs, it will fall like a log. 



Localization of Function in the Cerebellum. In birds and lower 

 vertebrates the cerebellum is only represented by the worm. Yet in 

 many of these animals the same characteristic disturbances follow its 

 removal as in the higher animals where the cerebellar hemispheres have 

 become so prominent. Indeed, it was mainly on the pigeon that 



