54 ESSENTIALS OF PHYSIOLOGY. 



column. It consists of long ascending fibres derived from the posterior 

 nerve roots ; these terminate in the medulla oblongata by arborisation 

 round the cells of the nucleus gracilis. The fibres of this tract are 

 situated first in the funiculus cuneatus ; as they ascend in the spinal 

 cord they come to lie nearer the middle line and more posteriorly, so 

 that in the cervical region those associated with the lower limb occupy 

 a position mesial and dorsal to those which have entered the spinal 

 cord at higher levels. 



The fibres of the funiculus cuneatus are also ascending, and are 

 derived from the posterior spinal nerve roots. Many of them terminate 

 by arborisation in relation with the cells of the nucleus cuneatus of the 

 medulla oblongata. Some, however, enter the grey matter of the 

 spinal cord itself. 



The bundle of Lissauer likewise consists of the ascending divisions of 

 posterior root fibres. These have a short course and terminate by 

 running into the grey matter of the spinal cord. Some authorities 

 consider that certain fibres of the tract of Lissauer are intersegmental 

 in character, because they acquire their myelin sheaths at a late stage, 

 and also because they do not degenerate under conditions which lead 

 to the degeneration of the other exogenous tracts, for example, in 

 locomotor ataxia. 



The chief endogenous ascending tracts are the direct cerebellar and 

 the antero-lateral ascending tracts, which lie in the peripheral part of 

 the antero-lateral column. 



The direct cerebellar tract (dorsal spino-cerebellar fasciculus) consists 

 of fibres which are the axons of cells in Clarke's column, and it is found 

 only in the thoracic and cervical regions. It runs through the medulla 

 oblongata and forms part of the restiform body, terminating finally in 

 the vermis of the cerebellum. 



The antero-lateral ascending tract (ventral spino-cerebellar fasciculus) 

 is found in the lumbar as well as in the thoracic and cervical regions. 

 Its fibres are derived from the cells of Clarke's column of the opposite 

 side, and it runs through the medulla oblongata and pons to the mid- 

 brain, where it turns round to form part of the superior cerebellar 

 peduncle, and ends in the vermis of the cerebellum. 



Associated with the ventral spino-cerebellar tract are two other 

 groups of fibres: (1) the spino-thalamic, which ascend through the 

 medulla oblongata, pons, and mid-brain to terminate in the thalamus, 

 and (2) the spino-tectal, which terminate in the corpora quadrigemina. 

 The ventral spino-cerebellar, spino-thalamic, and spino-tectal fasciculi 

 together form what was formerly known as Gowers' tract. 



