THE SPINAL CORD AS A CONDUCTOR 401 



especially in the posterior horns (cp. Fig. 161). The longest fibres pass 

 to the upper end of the cord, where they end in the posterior column 

 nuclei, the nucleus gracilis and the nucleus cuneatus of the medulla. 

 These fibres remain entirely on the side of the cord on which they 

 have entered. As they pass up they are displaced towards the middle 

 line by each incoming and higher placed root. Thus in the cervical 

 region, and indeed from the fifth dorsal segment upwards, two columns 

 can be distinguished in the posterior part of the cord, viz. the postero- 

 median and postero-lateral columns, the division between which is 

 indicated by a small groove on the surface. The postero-median 

 column contains from within outwards the fibres from the sacral region, 

 those from the lumbar region, and those from the inferior dorsal 

 region. The postero-lateral column, or column of Burdach, contains 

 mesially the four upper dorsal root fibres and more laterally the fibres 

 from the cervical nerves. 



(b) THE LATERAL COLUMNS. In these columns are found the 

 two cerebellar tracts, as well as scattered fibres passing to the fore- 

 and mid-brain. 



(1) THE DIRECT OR DORSAL CEREBELLAR TRACT arises from the 

 cells of Clarke's column on its own side. It consists of large fibres, 

 which pass through the grey matter to the lateral columns of the same 

 side, and ascend in the cord immediately ventral to the incoming 

 posterior root fibres, and external to the crossed pyramidal tract. In 

 the medulla they are joined by a bundle of fibres from the opposite 

 inferior olive and pass with the restiform body into the cerebellum, 

 where they terminate in the superior vermis of this organ. 



(2) THE VENTRAL OR ANTERIOR CEREBELLAR TRACT, often called 

 the tract of Gowers, arises in cells scattered through the grey matter, 

 chiefly of the posterior horn of the opposite side, though a few fibres are 

 derived from cells of the same side. The tract consists of fine fibres 

 which pass upwards in the peripheral margin of the lateral column, 

 extending from the direct cerebellar tract behind to the level of 

 the anterior roots in front ; it passes upwards through the cord, the 

 medulla, and the pons, then turns round to enter the cerebellum 

 through the superior cerebellar peduncle, ending chiefly in the ventral 

 portion of the superior vermis. 



(3) THE SPINO-THALAMIC AND SPINO-TECTAL TRACTS. These fibres 

 form a scattered bundle lying internally to the anterior cerebellar 

 tract, and are practically part of Gowers' tract. They may be traced 

 through the cord, medulla, and pons and end, partly in the anterior 

 corpora quadrigemina of both sides, but to a greater extent in the 

 optic thalamus of the same side. 



(c) ANTERIOR COLUMNS. A number of scattered fibres pass up 

 the anterior columns, mingled with the descending fibres of the tract 



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