CEREBELLUM, PONS, AND MEDULLA. 219 



superior peduncles end in the red nucleus of the midbrain on the 

 opposite side. Thence there may be connections forward with 

 the thalamus and cerebrum; but, what is more significant, con- 

 nections are thus made with the rubrospinal tract (Monakow's 

 bundle), see p. 169, which descends into the cord and connects 

 with the motor nerves. By this connection a relation may be es- 

 tablished between the cerebellum and the motor nerves of the body. 

 The path is doubly crossed, so that each cerebellar hemisphere is 

 connected with the muscles of its own side. Still another motor 

 path to the cord is made possible through the connections of the 

 vestibular nucleus. These latter, as stated on p. 170, are connected 

 through the vestibulospinal tract with the cells in the anterior 

 horn. Some authors have described a special motor tract from 

 cerebellum to cord, either direct or by way of the olivary bodies ; but 

 our knowledge of this path is too uncertain as yet to form a positive 

 basis for physiological conclusions. 



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 rhomme," 5, 418, 1862. 



