GERLACHS NETWORK AND MULTIPOLAR CELLS. 



629 



proceed upwards amongst the vertebrata. These cells usually contain pigment-grannies, and, 

 according to Pierret, their size has a direct relation to the length of the nerve-fibre proceeding 

 from them ; so that they are largest in the lumbar enlargement, smaller in the cervical enlarge- 

 ment, and smallest in the dorsal region. Smaller spindle-shaped (" sensory " ) cells occur in 

 much smaller numbers in the grey matter of the posterior horn. The cells of Clarke's column 

 (fig. 445) are smaller (30-60 /*), and are usually arranged with their long axis in the long axis of 

 the cord. The processes are fewer, but one is generally directed towards the head, and some 

 towards the caudal end of the body. They usually contain much pigment, which is generally 

 disposed towards the cerebral pole of the cell.] 



[In a longitudinal section of the cord (fig. 447), these cells are seen to be arranged in columns, 

 the large multipolar cells in the anterior horn (m) ; in the same section are shown, the longi- 

 tudinal direction of the nerve-fibres in the anterior (a) and posterior white columns (c), the 

 horizontal direction of the fibres of the anterior and posterior nerve-roots (b and/). 



The grey matter contains an exceedingly delicate fibrous network of the finest nerve-fibrils 

 (Gerlach), which is produced by the repeated division of the protoplasmic processes of the 



* P.M.F. 



Fig. 445. Fig. 446. 



Fig. 445. Nerve-cell from Clarke's column (horse). The arrow indicates the cerebral end. Fig. 

 446. Transverse section of the spinal cord (lower dorsal). A, L, P, anterior, lateral, and 

 posterior columns; A.M.F., P.M.F., anterior and posterior median fissures; a, b, c, ceils 

 of the anterior horn ; d, posterior coma and substantia gelatinosa ; e, central canal ; /, 

 veins ; g, anterior root bundles ; h, posterior root bundles ; i, white commissure ; ,/, grey 

 commissure ; I, reticular formation. 



multipolar ganglionic cells. Medullated nerve-fibres traverse and divide in the grey matter 

 and become non-medullated; some of them merely pass through the grey matter of the non- 

 medullated fibres and terminate in Gerlach's network. Fibres pass from the grey matter of one 

 side to that of the other through the commissures in front of and behind the central canal. 



[By means of Weigert's method of staining medullated nerve-fibres (p. 529), it has been 

 proved that numerous, fine, medullated nerve-fibres exist in the grey substance. ] 



Gerlach's Theory. According to Gerlach, the connection of the fibres and cells is as follows : 

 The fibres of the anterior root proceed directly to the ganglionic cells of the anterior horn, 

 with which they form direct communications by means of the unbranched axial cylinder pro- 

 cesses (fig. 448, z). The grey network of protoplasmic processes, produced by the repeated 

 branchings of the fibres of these cells, gives origin to broad fibres. A part of the latter (the 

 median bundle) passes through the anterior white commissure to the other side, and then ascends 



