220 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



medullary substance of the vermiform lobe (nucleus fastigii, n. 

 globosi, and the n. embolif ormis) . The axons of the Purkinje 

 cells of the cortex terminate in these subcortical nuclei, and the 

 efferent path from the cerebellum is then continued by new neurons. 

 Thus, the fibers of the superior peduncles of the cerebellum arise 

 chiefly from the dentate nuclei, and only indirectly from the cor- 

 tex. The anatomical connections, afferent and efferent, between 

 the cerebellum and other parts of the nervous system are very com- 

 plex and not yet entirely known. Without attempting to recall 

 all of these connections, which will be found described in works upon 

 anatomy or neurology, emphasis may be laid upon those which are 

 at present helpful in discussing the physiology of the organ. 



1. Connections with the Afferent Paths of the Cord. Through 

 the inferior peduncles the cerebellum receives afferent fibers from the 

 spinal cord and the medulla. The tract of Flechsig undoubtedly 

 terminates in the cerebellum, and according to some observers the 

 fibers of the posterior columns after ending in the n. gracilis and 

 n. cuneatus are continued in part to the cerebellum by nerve fibers 

 passing by way of the inferior peduncles. Ascending fibers arising 

 in the reticular formation of the medulla and the olivary nucleus 

 also take this path to the cerebellum, and, on the other hand, prob- 

 ably make connections with the sensory tracts of the cord or the 

 sensory nuclei of the medulla. Another afferent tract of the cord, 

 that of Gowers, enters the cerebellum by way of the superior 

 peduncles. The nature of the sensory impulses conveyed in this 

 way to the cerebellum is not entirely understood, but it seems 

 certain that some of them, at least, are what we designate as im- 

 pulses of the muscle sense, and this fact, as we shall see, throws 

 some light on the specific functional importance of the cerebellum. 



2. Connections with the Vestibular Branch of the Eighth Cranial 

 Nerve. This branch, arising in the semicircular canals and utriculus 

 and sacculus, ends in the pons in several nuclei (Deiters', Bech- 

 terew's) and also in the n. fastigii of the cerebellum. These nuclei 

 in turn are connected with other parts of the central nervous system, 

 but the details are not yet completely known. The connections 

 that have been most clearly established are those made with the 

 motor centers. From Deiters' nucleus the vestibulospinal tract 

 arises and passes to the cord to connect with the motor centers of 

 the spinal nerves, while Bechterew's nucleus is said to give origin 

 to a bundle which runs with the posterior longitudinal fasciculus 

 and may make connections with the motor nuclei of the cranial 

 nerves. In how far the vestibular nuclei may make afferent con- 

 nections with the cerebellum is undecided, but it seems probable 

 that such tracts exist, in view of the fact that destruction of the 

 semicircular canals and severe lesions of the cerebellum cause 

 motor disturbances that are strikingly similar. 



