222 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



by way of the thalamus. Fibers arising in the dentate nucleus 

 emerge by way of the superior peduncles and connect with the 

 red nucleus in the subthalamic region and perhaps also with the 

 thalamus. The latter fibers may be continued forward to the 

 cortex of the cerebrum and thus constitute an afferent 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. 98). 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 in 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, 

 especially 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 

 for the muscle sense. This view is connected usually with the name 

 of Lussana,* but has been supported since in one sense or another 

 * Lussana. See " Journal de la physiol. de I'homme," 5, 418, 1862. 



