626 Dynamic Theory. 



alone. But without the cerebellum they are largely, if not entirely, 

 unbalanced, and unmodified by each other. The stimuli which are thus 

 balanced in the cerebellum, include, beside those of touch and heat, 

 those of sight and hearing, and no doubt also those of smell and taste, 

 in short, all the sense stimuli, for all are concerned and employed in 

 the modification of muscular movement. 



The cerebellum is the third complete organic machine for the conver- 

 sion of afferent nervous stimulations into motor and muscular action, 

 the spinal cord and the medulla oblongata being, respectively, numbers 

 one and two. It is far more complicated in its operations because these 

 operations result from the combination of a greater number of stimuli. 



The tactile sense, including that of heat and pressure, and the mus- 

 cular sense, are the only ones which impress themselves on the spinal 

 cord through the nerves of "general sensibility." The medulla ob- 

 longata is subject to the impressions of the stimuli from a greater num- 

 ber of sources, and its resulting reactions are of a correspondingly more 

 varied and complicated character. 



The cerebellum is greatly in advance of the medulla oblongata in the 

 number of stimuli by which it is competent to be impressed, and per- 

 haps in the kind of stimuli, too. The medulla contains the detached 

 nuclei of various encephalic nerves, nuclei which form more or less 

 complete centers for the conversion of the afferent stimuli of the nerves 

 into the corresponding motor stimuli of the same, but there is not the 

 same combination of nuclei and co-ordination of various kinds of stim- 

 uli that occur in the cerebellum. Each system is independent of the 

 one below it, and, if not interfered with by the one above it, is compe- 

 tent to act alone. It is probable, if not certain, that both the motor 

 and sensory tracts of each is independent of those of the other. 



The cerebellum appears to be, in some respects, a cross or intermedi- 

 ate organ between the medulla oblongata and the cerebrum, possessing 

 internal nuclei like the former, and a cortex of gray matter like the lat- 

 ter. It is like the cerebrum in the fact that it cannot be stimulated to 

 normal action by mechanical or chemical irritations, but does respond 

 normally to the stimulus of the galvanic induction current. 



CHAPTER LXIL 



FUNCTIONS OF THE BASAL, GANGLIA. 



The Basal Ganglia consist of several ganglia of brain substance lying 

 under and within the shell of the cerebral hemispheres. They serve 

 two functions, sensory and motor. The sensory ganglia are the corpora 

 quadrigemina, optic thalamus, and probably the pineal gland, or cona- 

 rium. The motor ganglia are the corpora striata. 



