via THE HIND-BKAIN 473 



Both the trophic and the tonic influences are continuously 

 excited by the direct and indirect paths that carry impulses to 

 the cerebellum from the cutaneous, muscular, and labyrinthine 

 sense-organs. Of these afferent paths that serve the activity of 

 the cerebellum, particular importance attaches to the vestibular 

 nerve, which transmits tonic impulses from the labyrinth by way 

 of the nucleus of Deiters, as demonstrated by Ewald, Gaglio, 

 Stefani, and Deganello. It must be abmitted that the demonstra- 

 tion of the special influence which the labyrinth exerts on the 

 functions of the cerebellum is the only new fact of real importance 

 that has been added to the physiology of this organ. 



X. In conclusion we must recapitulate the new morphological 

 theory of the cerebellum, which Bolk has constructed on the basis 

 of an interesting phylogenetic and ontogenetic comparison between 

 the brains of different mammals and man. 



From the phylogenetic point of view, the cerebellum of all 

 mammals consists of two lobes, one anterior, the other posterior, 

 divided by a primary sulcus. The anterior lobe always forms a 

 single unpaired median organ ; the posterior lobe is subdivided 

 into four lobules, two median and two lateral, which are separated 

 by secondary sulci. 



From the ontogenetic point of view, Bolk distinguishes four 

 centres of development, two median and two lateral, characterised 

 by varying rapidity of growth, during which the lobular arrange- 

 ment of the adult cerebellum is determined by means of numerous, 

 mainly transverse sulci. 



On studying the developmental variations of the single lobes 

 or lobules of the cerebellum in different mammals, Bolk noted a 

 more or less definite relation between them and the degree of 

 functional development of special groups of muscles ; this led him 

 to attribute the functional control of special muscular complexes 

 to certain lobules. 



We must confine ourselves to the main features of the 

 functional localisations in different lobules of the cerebellum, 

 based on the ingenious deductions made by Bolk from his morpho- 

 logical studies. 



He starts from the fact, that in certain movements the 

 muscles on both sides come into action, and in other parts of 

 the body the muscles of one side are capable of the most complex 

 movements, while those of the other side may remain altogether 

 inactive. 



The head and neck are certainly included among the former. 

 In the head are the external muscles of the eyes, the masticator 

 muscles, the mimic facial muscles, the lingual, pharyngeal, and 

 laryngeal muscles, which nearly always function bilaterally. In 

 the neck, again, the muscles that effect the various movements of 

 the head enter into bilateral activity. The muscles of both the 



