332 PRACTICAL HISTOLOGY. [XXX. 



antero-laterul. It enters the cerebellum by the superior cerebellar 

 peduncle. 



In the dog, as a result of excision of one-half of the cerebellum, 

 a circumferential tract, occupying three-fourths of the surface of the 

 antero-lateral tract the antero-lateral descending cerebellar tract 

 has been mapped out. The remainder of the antero-lateral column 

 is spoken of as the antero-lateral ground bundle. 



As regards the results of degeneration following section or lesion 

 of the cord, those parts that undergo degeneration above the lesion 

 are called "ascending tracts"; and "descending tracts," are those 

 nerve-fibres that degenerate below the lesion or seat of section. 

 The parts which may undergo these respective degenerations are : 



( Direct pyramidal tract. 

 Descending \ Crossed pyramidal tract. 



degeneration 1 Autero-lateral descending cerebellar tract (limited). 

 I Com ma tract. 

 ( Goll's column. 



Ascending \ Direct cerebellar tract. 



degeneration, j Tract of Gowers. 

 L Tract of Lissauer. 



It will thus be seen that in the antero-lateral columns there are 

 some nerve-fibres which do not undergo degeneration. 



Course of Fibres of Nerve-Roots. The fibres of the anterior 

 roots arise in several bundles from the axis-cylinder processes of the 

 multipolar nerve-cells in the anterior cornu. 



The fibres of the posterior roots enter the cord by a single bundle, 

 but each one is an axial cylinder process of a nerve-cell in the 

 corresponding spinal ganglion. They pass into the postero-lateral 

 column, some pass into the posterior cornu, and a few small fibres 

 form the marginal bundle (p. 331). Many fibres pass up in Goll's 

 column, and the postero-external tract to end in terminal arborisa- 

 tions of fibrils around nerve-cells in the bulb, the fibres of Goll's 

 column in arborisations around the cells of the nucleus gracilis, and 

 those of the postero-external tract in the nucleus cuneatus. After 

 entering the cord, the fibres in the posterior columns bifurcate, one 

 branch passes upwards and one downwards (fig. 322). Collateral 

 fibres are given off from the original fibre, and also from its 

 branches,- which enter the grey matter and end by terminal arbori- 

 sations of fine fibrils which come into relation but not direct union 

 with the nerve-cells of the grey matter, notably with the colls 

 of Clarke's column. 



THE SPINAL CORD. 



It is convenient to begin with the cord of a small animal, e.//., a 

 cat or dog, but the student must also be provided with sections of 



