THE CENTRAL NERVOUS SYSTEM. ^OI 



the cord and those arising from the medulla. The first group 

 comprises : 



(a) The direct upward continuation of the postero-external (Bur- 

 dach's) column. 



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



(c) The fibres of the postero-median (Coil's) tract of the posterior 

 column ; this latter is prolonged into the posterior pyramid, which, 

 in turn, is absorbed by the restiform body. 



Those arising within the medulla are : 



(of) The fibres of the funiculus Rolandi. 



(<?) The fibres contributed by the anterior pyramid. 



(/") Some arcuate fibres issuing from the anterior median fissure. 



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 with its contained 

 nucleus, and then, diverging from its fellow of the opposite side, tapers 

 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 commissural tracts 

 connecting the hemispheres of the 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 to 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, the dorsal or deep bundles, and the middle or 

 penetrating bundles. 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 



