234 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



line and to the cerebellar cortex by way of the middle peduncle 

 (brachium pontis). The tract would seem to convey efferent 

 impulses from the cerebral cortex (motor region) of one side to 

 the cerebellar cortex of the opposite side. 



5. Efferent Paths from Cerebellum. — Fibers arising in the den- 

 tate nucleus emerge by way of the brachium conjunctivum and 

 connect with the red nucleus in the subthalamic region and per- 

 haps also with the thalamus. The latter fibers may be continued 

 forward to the cortex of the cerebrum and thus constitute a path 

 from cerebellum to cerebrum. Those fibers, on the contrary, which 

 end in the red nucleus are brought into reflex connection with the 

 motor bundle (rubrospinal tract), extending from the red nucleus 

 to the motor centers in the spinal cord. Making use of the connec- 

 tions described above, Van Gehuchten pictures an indirect motor 

 path from the cortex of the cerebrum to the motor nerves by way 

 of the cerebellum (see Fig. 104). The motor impulses descend by 

 way of the cortico-ponto-cerebellar path to the cerebellar cortex, 

 thence to the dentate nucleus, thence to the red nucleus, and then, 

 by way of the rubrospinal tract, to the motor nuclei of the spinal 

 nerves. 



Theories Concerning the Functions of the Cerebellum.— 

 Modern views concerning the functions of the cerebellum may be 

 classified under three general heads: First, those that consider it 

 a general co-ordinating center or organ for the muscular movements 

 and especially for those concerned m equilibrium and locomotion. 

 This view, first proposed essentially by Flourens (1824), has been 

 adopted by many, perhaps by most, writers since his time. The 

 manner in which the organ serves to co-ordinate these movements 

 has been explained in various ways. According to the older ob- 

 servers, it was supposed so to arrange or group the various motor 

 impulses that they reached the lower motor centers in the cord 

 in the necessary combination for co-ordinated contractions. Ac- 

 cording to more recent observers, this synergetic action is exer- 

 cised not directly on the motor side of the reflex but on the sensory 

 side. The numerous sensory paths connected with the organ, es- 

 pecially those of the muscular sense, and those from the vestibular 

 nerve, suggest the view that in the complex cortex of the cerebel- 

 lum these afferent impulses act upon nervous combinations whose 

 discharges, in turn, are conveyed to the motor centers in a definite 

 and orderly sequence. Either point of view assumes that there 

 are in the cerebellum certain distinct mechanisms — that is, combi- 

 nations of neurons — that are essentially reflex centers, and that in 

 all of our more complex bodily movements these mechanisms 

 intervene. The second general set of theories regarding the cere- 

 bellum assumes that this organ is essentially the center or a center 



