THE NERVOUS SYSTEM 



1325 



fibres of the dorsal roots of the lower spinal nerves enter the column 

 of Goll. 



The ascending and descending branches give off numerous 

 collateral fibrils, which enter the dorsal cornu. These collaterals 

 have the following destinations : (i) The dorsal cornu of the same 

 side, and that of the opposite side through the dorsal or grey com- 

 missuje; and (2) the ventral and lateral cornua of the same side. 

 In each case they come into close relation with the corresponding 

 nerve-cells — e.g., the cells of the dorsal cornu, including Clarke's 

 column, the ventral or motor-cells of the ventral cornu, and the 

 cells of the intermedio-lateral tract of Clarke in the lateral cornu. 



Multipolar Cells of Anterior Cornu 



Fibres of Motor Root 



Compound Spinal Nerve { 



Efferent and Sensory Fibres of Ganglion ; Afferent Fibres of Ganglion 



Spinal Ganglion witb two Bipolar Cells 



Fig. 555. — Origin of Motor and Sensory Fibres of a Spinal Nerve. 



Spinal Ganglia. — These are situated on the posterior roots of the 

 spinal nerves in the intervertebral foramina, and outside the theca, 

 though invested by a prolongation from it. Each ganglion is oval, 

 and consists of unipolar nerve-ceUs. The single pole of each cell 

 divides into two processes, one of which is centripetal and forms part 

 of the posterior nerve-root, whilst the other is centrifugal and passes 

 into the spinal nerve. The pole and its inward and outward pro- 

 cesses resemble the letter T. In early Ufe the cells are bipolar. 



The fibres of the posterior ner\-e-roots have their deep origins in 

 the unipolar cells of the spinal gangUa, and they grow into the spinal 

 cord. On the other hand, the fibres of the anterior nerve-roots 

 have their deep origins within the spinal cord, where they arise 

 as the axons of the multipolar nerve-cells of the anterior cornu of 

 grey matter, and they grow outwards. 



Tracts of the Spinal Cord. 



Posterior Column. — The tracts of this column are ascending and 

 descending, and they are as follows: 



Ascending Tracts. Descending Tract. 



Tract of GoII. Comma Tract ol Schultz. 



Tract of Burdach. 

 Tract of Lissauer. 



This tract also belongs to the lateral column. 



