THE NERVOUS SYSTEM 513 



ary tracts to the thalamus {via fillet and also in reticular formation?) form part 

 of the trigeminal afferent pallial path. 



The superior terminal vestibular nucleus (of von Bechterew) may still be 

 present. The superior olivary and trapezoid nuclei may be present. The 

 secondary (and tertiary (?), see Fig. 338) cochlear tract or lateral lemniscus is 

 now well formed and may be seen lying dorso-lateral to the superior olivary and 

 trapezoid nuclei. 



The medial lemniscus is still more llattened. The spino-thalamic and ventral 

 spino-cerebellar tracts occupy the same positions. 



Other Afferent Cerebellar Neurones. — The transverse pons fibres are the 

 same, but the longitudinal fibres have increased owing to the presence of more 

 pallio-pontile fibres. The perpendicular pontile fibres are seen passing dorsal ly in 

 the raphe into the tegmentum. 



The central tegmental tract is in nearly the same position. 



Intersegmental Neurones. — The reticular formation is somewhat diminished. 

 In it is the nucleus reticularis tegmenti. The rubro-spinal tract is in the same 

 position, mingled v.-ith the spino-thalamic and ventral spino-cerebellar tracts. 

 The medial longitudinal fasciculus is unchanged. 



Efferent Suprasegmental Neurones. — The pyramids now occupy the cen- 

 tral part of the pons, and are broken up into a number of bundles. In the 

 dorsal part of the pons fibres pass obliquely dorsally. These are probably 

 efferent pallial fibres which act directly or indirectly on some of the efferent 

 nuclei of cranial nerves (motor path to cranial nerves). The pallio-pontile 

 fibres have been mentioned. 



The superior peduncle is now a large bundle of fibres flattened against the 

 ventricular surface of the dorso-lateral brain wall. 



The colliculo-spina' tract is in the same position. 



Cerebellum 



The cerebellum, connected with the rest of the brain by its three 

 peduncles, consists of two lateral lobes or hemispheres connected by a 

 median lobe, the vermis. These are divided into various lobules, the 

 surfaces of which are marked by parallel transverse folds or laminae. 

 When these are cut across it is seen that they give off secondary 

 or tertiary laminae, the whole producing the appearance known as the 

 arbor vitas. The surface of the cerebellum is composed of gray matter, 

 the cortex, enveloping the white matter. Besides this there are 

 masses of gray within, the internal nuclei of the cerebellum (dentatus, 

 globosus, emboliformis, and fastigii), embedded in its white matter. 

 Fibres entering the cortex are the terminations of the fibres of the 

 restif orm body (dorsal spino-cerebellar tract to the cortex of the vermis, 

 olivo-cerebellar fibres to the whole cortex, fibres from the ateral 

 nucleus and possibly other nuclei in the reticular formation, also per- 



33 



