Tin: r /;/,- /;/.' /;/./. r.u 793 



inferior, middle, and superior. The three peduncles of e:ich side come together at 

 the level of the lower border of the pons, and the entering and emerging fibres of 

 which they are composed become continuous with the central core of white substance 

 of t lie cerebellar hemispheres. 



The restiform body of the medulla oblongata is the inferior peduncle. It forms 

 the lateral boundary of the inferior portion of the fourth ventricle, and upon reaching 

 the level of the pons turns sharply backwards into the cereU'llum. In the region of 

 the turn it is encircled externally by fibres of the cochlear division of the eighth 

 cranial nerve. It contains fibres, both ascendinir and descending, bet ween the 

 cerebellar cortex and the structures below the cerebellum: (1) Fibres from the 

 spinal cord including the lateral cerebello-spinal fasciculus (direct cerel>ellar tract) and 

 probably a small proportion of the ascending fibres of the antero-lateral superficial 

 fasciculus ((lowers' tract); (2) fibres from the olive of the same and opposite side 

 of the medulla oblongata; (3) fibres from the nuclei of the funiculus gracilis and 

 cuneat us of the same and opposite sides; (4) fibres to the olive of the opposite side; 

 (5) fibres to the nuclei of the motor cranial nerves; (6) fibres descending to the ven- 

 tral horn cells of the spinal cord. The ascending or afferent fibres of the cerebello- 

 spinal and cerebello-olivary fasciculi are the principal components of the inferior 

 peduncle. Of these, the fibres of the direct cerebellar tract terminate in the cortex 

 of the superior vermis of both sides of the mid-line, but, for the most part, in that 

 of the opposite side. The olivary fibres end in the cortex of both the superior 

 vermis and the adjacent cortex of the hemispheres, and some of them terminate 

 in the nucleus dentatus. 



The brachium pontis or the middle peduncle is the largest of the three cerebellar 

 peduncles. In it the pons fibres pass slightly downwards and into the cerebellar 

 hemisphere, between the lips of the anterior part of the horizontal fissure, entering 

 at the outer side of the inferior peduncle. It consists of the transverse fibres of the 

 pons, and within the cerebellum its fibres are distributed in two main groups the 

 upper transverse fibres of the pons apparently pass downwards to radiate in the 

 lower portion of the hemisphere, while the lower transverse fibres pass upwards and 

 inwards to radiate in the superior part of the hemisphere and vermis. For the most 

 part the fibres of the middle peduncle may be considered as commissural fibres, 

 passing from one side of the cerebellum to the other. Each peduncle contains 

 fibres coursing in opposite directions. Many of these fibres are interrupted in their 

 course to the opposite side by cells scattered throughout the pons, nuclei pontis, and, 

 therefore, in each brachium pontis some of the fibres are processes of the cells of the 

 cerebellum and course towards the opposite side, while others are processes of the 

 cells of the pontine nuclei and course to the cerebellar hemisphere of the same side. 

 Furthermore, there are evidences after degeneration that the brachium pontis also 

 contains a few fibres from the cerebellum to the structures of the brain-stem and 

 spinal cord. 



The brachium conjunctivum or superior cerebellar peduncle emerges from the 

 cerebellum on the inner side of the brachium pontis. It also extends on the mesial 

 side of the course of the restiform body. It forms the lateral boundary of the supe- 

 rior portion of the fourth ventricle. Its transverse section appears semilunar in 

 shape, with the concave side next to the cavity of the ventricle. The dorsal border 

 which inclines towards the mid-line is connected with that of the corresponding 

 peduncle of the opposite side by the anterior medullary velum, which thus roofs over 

 the superior part of the fourth ventricle. The ventral border is distinguished from 

 the pons by an open furrow or sulcus. 



The superior cerebellar peduncles are almost entirely efferent pathways as to the 

 cerebellum, and form the chief connections between the cerebellum and the cerebrum. 

 They arise almost wholly from the dentate nuclei. As they course forwards they 

 slightly converge and disappear under the inferior quadrigeminate bodies. Here, 

 in the tegrnentum of the rnesencephalon, they undergo an almost total decussation, 

 and then the majority of the fibres of each peduncle, having thus crossed the mid- 

 line, terminate in the m/ //W/O/N of the opposite side. The red nucleus lies in the 

 tegmentum of the mesencephalon. below the superior i|iiadrigeminate bodies, and 

 therefore quite close to the decussation. The cells of the red nucleus, about which 

 the fibres of the peduncle terminate, in their turn send processes (axones) into the 

 prosencephalon. most of which enter the thalamus, but some pass under the thalamus 

 to join the internal capsule. 



