CH. XLV.] 



PEDUNCLES OF CEREBELLUM 



651 



possessing bunches of short branches at intervals (moss-fibres of 

 Oajal). 



The peduncles of the cerebellum are three in number superior, middle, and 

 inferior ; we have already had occasion to mention them in our study of the bulb, 

 pons, and mid-brain. The course of the fibres has been studied by the degenera- 

 tion method. The superior peduncle consists mainly of fibres which originate in 

 the corpus dentaturn ; some fibres are said to arise in the cerebellar hemisphere, 

 and to pass through the corpus dentatum without communicating with its cells. 

 These fibres cross the raphe in the mid-brain, and terminate in the red or tegmental 

 nucleus. The direction of the impulses in these fibres is from cerebellum to 

 cerebrum, the red nucleus being a cell station on the road. There appear, however, 

 to be some fibres starting from the optic thalamus which convey impulses in the 

 opposite direction. In addition to these there is Cajal's descending cerebellar bundle. 



I. 



II. 



FIG. 473. Section of cerebellar cortex, stained by Golgi's method ; i. taken across the lamina ; n. in 

 the direction of the lamina; A, outer or molecular layer; B, inner or granular layer ; c, white 

 matter, a, Cell of Purkinje ; b, small cells of inner layer ; c, dendrons of these cells ; d, axis- 

 cylinder process of one of these cells becoming longitudinal in the outer layer ; e, bifurcation of one 

 of these ; g, a similar cell lying in the white matter. (Ramon y Cajal.) 



This consists of branches which are given off by the fibres before they cross at the 

 raphe ; they pass towards the bulb, giving off collaterals to the motor nucleus of the 

 fifth nerve, to the facial nucleus, to the nucleus ambiguus, and others. One must 

 not forget that besides all these fibres that the tract of Cowers joins the superior 

 peduncle, and runs back along its mesial border to the vermis. 



The middle peduncle consists of fibres which form the anterior transverse fibres 

 of the pons. They pass from the nuclei pontis to the opposite cerebellar hemi- 

 sphere. Others convey impulses in the opposite direction from the hemisphere to 

 the pons ; on section, these fibres degenerate as far as the raphe, where they inter- 

 mingle with those from the opposite side. 



The inferior peduncle or restiform body is composed of ascending fibres, which 

 pass into it from the direct cerebellar tract, from both olivary nuclei, but mainly 

 from that of the opposite side, from the nucleus gracilis and nucleus cuneatus, and 

 from the nuclei of the sensory roots of the cranial nerves. The fibres pass mostly 

 to the vermis, crossing to the opposite side over the fourth ventricle, but giving off 

 strong collaterals to the cerebellar hemisphere of the same side ; these account for 

 the fact that each cerebellar hemisphere is in principal physiological connection with 

 the same side of the spinal cord. 



