CHAPTER XII 



THE CEREBELLUM. THE MEDULLA AND MIDBRAIN. THE 

 SYMPATHETIC SYSTEM 



The Cerebellum. This organ, as shown in Figs. 60, 61, is a dis- 

 tinct portion of the brain, lying underneath the posterior part of 

 the cerebrum, and behind and above the midbrain and medulla. 

 It consists, as does the cerebrum, of cortical gray matter super- 

 posed upon white matter, and having imbedded within the white 

 matter at its base gray masses, the nuclei of the cerebellum. Like 

 the cerebrum also, its cortex has afferent and efferent nerve con- 

 nections with the rest of the central nervous system. From this 

 anatomical structure we are led to conclude that the cerebellum 

 is probably as is the cerebrum, the seat of complicated reflex 

 actions. When we examine the afferent tracts leading to the 

 cerebrum we are struck with the high degree to which afferent 

 tracts from certain senses are developed and the smallness or ab- 

 sence of tracts from other senses. The most conspicuous afferent 

 tracts of the cerebellum are the tracts of body sense; these pass 

 up the spinal cord along its lateral margins (Fig. 66). They arise 

 from cell-bodies lying along the cord in its gray matter and hav- 

 ing dendrites doubtless in synaptic connection with collateral ter- 

 minations of sensory neurons. As these tracts reach the medulla 

 there is a branching on each side into two bundles of fibers; the 

 dorsal bundle passes directly from the medulla to the cerebellum 

 by way of the lower supporting stalk of the cerebellum, the inferior 

 peduncle; the ventral bundle passes further along to the upper 

 supporting stalk, the superior peduncle, through which it reaches 

 the cerebellum. 



There is reason to think that two of the body senses, muscle 

 sense and touch (Chap. XIII), are in specially close communi- 

 cation with the cerebellum through these tracts. 



Another sense which seems to have particularly abundant 

 communication with the cerebellum is the equilibrium sense 

 (Chap. XIV). This sense is mediated by the semicircular canals 



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