THE CENTRAL NERVOUS SYSTEM. 



from the cord and the medulla and those arising from the 

 pons. The first group comprises : 



(a) The direct cerebellar tract of the lateral column. 



() The posterior external arcuate fibres from the nucleus gracilis 

 and nucleus cuneatus of the same side. 



(V) The anterior external arcuate fibres from the nucleus gracilis 

 and nucleus cuneatus of the opposite side. 



(d) The internal arcuate fibres from the inferior olive of the oppo- 

 site side. 



O) Fibres from the lateral nucleus of the medulla. 



The pontine group includes : 



(/) Fibres from the superior olive of the opposite side. 



() Fibres from the acoustic nucleus of the same side. 



4. The posterior pyramid is the upward prolongation of the 

 postero-median column of the cord. On approaching the lower 

 angle of the fourth ventricle, this column, or the funiculus gracilis, 

 exhibits the pronounced thickening of the clavus, which contains the 

 nucleus gracilis and then merges into the restiform body. 



THE PONS. 



The pons, as may be inferred from the mutual relations of the sev- 

 eral divisions of the brain which it connects, consists very largely of 

 bundles of nerve-fibres ; in addition to these, areas of gray mat- 

 ter, the pontine nuclei, supplement the nerve-fibres in making up 

 its mass. On section the pons exhibits two portions, the dorsal and 

 the ventral. The latter contains the principal decussating tracts 

 connecting the cerebral cortex and cerebellum, and constitutes a 

 robust mass of transverse fibres ; through this the longitudinal 

 bundles of the anterior pyramids of the medulla force their way in 

 their course from the cerebrum. In the lower half of the pons the 

 pyramidal fibres are collected into two closely- packed groups of 

 bundles, one on either side of the mid-line, which are enveloped in 

 front and behind by a layer of transverse fibres ; higher up, above 

 the middle of the pons, the pyramidal tracts become separated by the 

 penetrating transverse bundles into a number of fasciculi. Among 

 the transverse tracts, therefore, are recognized the ventral or super- 

 ficial bundles and the dorsal or deep bundles, the latter forming 

 the corpus trapezoideum. Small multipolar cells are found 

 widely distributed in the ventral region of the pons within the gray 

 matter which occupies the interfibrillar interstices. 



The dorsal portion of the pons consists largely of structures rep- 

 resenting the continuation of parts already encountered below, espe- 

 cially of the formatio reticularis and of the dorsal tracts of gray 

 substance. In addition to the gray matter scattered throughout 



