CEREBELLUM, PONS, AND MEDULLA. 237 



and that similar paths extend from the primary end stations of 

 the optic fibers.* 



4. Connections with the Cortex of the Cerebrum. The cerebellar 

 cortex is connected with the cerebral cortex by the large system 

 known as the cortico-ponto-cerebellar tract (see Fig. 82, A). The 

 fibers of this tract arise in the motor area of the cerebrum or in the 

 frontal cortex anterior to the motor area, descend in the internal 

 capsule and cerebral peduncle, and end in the gray matter of 

 the pons. Thence new axons continue the path across the 

 mid-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. A second 

 possible connection with the cerebrum is made by way of the 

 thalamus. Fibers arising in the dentate nucleus emerge by 

 way of the brachium conjunctivum 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. 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 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 

 * See Edinger, " Brain," 29, 483, 1906. 



