206 THE NERVOUS SYSTEM 



fibers of the vestibular nerve and constitute the tractus vestibulocerebellaris . 

 According to Cajal (1911) the fibers of this tract are distributed to the cortex 

 of the cerebellum, the majority of them going to the vermis, a smaller proportion 

 to hemisphere. In view of the newer ideas concerning the morphology of the 

 cerebellum, the statements concerning the termination of all these cerebellar 

 afferent fibers require re-examination. 



The brachium conjunctivum (Fig. 88) consists of efferent fibers from the 

 dentate nucleus to the red nucleus and the thalamus of the opposite side. It is 

 the smallest and most medial of the three peduncles. The ventral spinocere- 

 bellar tract enters the cerebellum in company with the brachium conjunctivum. 

 It ascends through the medulla oblongata and pons, curves over the brachium 

 conjunctivum (Fig. 110), and enters the anterior medullary velum, within which 

 it runs to the cerebellum (Fig. 149). Its fibers terminate in the rostral part of 

 the vermis and in the nucleus fastigii (Horrax, 1915). According to Edinger, 

 a bundle of fibers, the tectocerebellar tract, arises in the tectum of the mesencepha- 

 lon and descends alongside of the brachium conjunctivum to the cerebellum, 

 probably conveying impulses from visual centers. 



According to MacNalty and Horsley (1909) and Ingvar (1918) the fibers of the ventral 

 spinocerebellar tract end in the lobulus centralis, culmen, and most rostral part of the declive. 

 The fibers of the dorsal spinocerebellar tract have the same termination and, in addition, 

 many of them go to the pyramis, and smaller numbers to the uvula and nodule. Practically 

 all of the fibers which end in the cortex, therefore, go to the anterior and posterior lobes 

 (Ingvar). The fact that the anterior lobe receives the majority of these fibers, which convey 

 proprioceptive impulses from the trunk and extremities, is a strong argument against Bolk's 

 conception of the anterior lobe as a co-ordination center for the musculature of the head. 



HISTOLOGY OF THE CEREBELLAR CORTEX 



The cerebellar cortex differs from that of the cerebral hemispheres in pos- 

 sessing essentially the same structure in all the lobules. This would indicate 

 that it functions in essentially the same way throughout, though as a result of 

 different fiber connections the various lobules act on different muscle groups. 



A section through the cerebellum, taken at right angles to the long axis 

 of the folia, shows each folium to be composed of a central white lamina, covered 

 by a layer of gray cortex. Within the white lamina the nerve-fibers are arranged 

 in parallel bundles extending from the medullary center of the cerebellum into 

 the lobules and folia. A few at a time these bundles turn off obliquely into the 

 gray matter, and there is no sharp demarcation between the cortex and the sub- 

 jacent white lamina. The cortex presents for examination three well-defined 



