334 



MANUAL OF HISTOLOGY. 



ing and winding in every possible direction between the cells of the latter. 

 Eventually, however, they become again united into bundles, which asso- 

 ciate themselves with those which passed through in a straight line. In 

 this way are formed the stem or stems which leave the ganglion (d, e). 



The nerve fibres entering the knots have, on this account, been classed 

 into " direct" and " tortuous," terms which will still be found appropriate. 

 There exist, however, as might be supposed, many intermediate forms 

 between the two modes of arrangement. 



It used formerly to be believed that the relation of the fibres to the 

 cells within the ganglion was only that simply of close proximity. This 

 view, however, was found to satisfy the requirements of the physiologist 

 just as little as that which held that the nerve-fibres ended in loops, and 

 was finally abandoned on the discovery of the origin of the fibres. 



Confining ourselves for the present to the spinal ganglia (fig. 319), we 



find that a number of investigators have 

 observed an extraordinary arrangement in 

 these structures in the fish, namely, that 

 all the nervous fibres of the posterior root 

 of the ganglion are interrupted in their 

 course within the latter by a cell, the 

 broader fibres usually by a larger, the 

 finer by a smaller element. 



The corresponding ganglia of mam- 

 mals and man, however, present but 

 rarely such bipolar cells (7i). Here 

 some of the processes may take an op- 

 posite course, as in the fish, or both pass 

 out below towards the periphery (a). As 

 a rule, we meet with nerve cells here which 

 only give off one process towards the cir- 

 cumference (/), which may subsequent- 

 ly divide into two fibres, according to 

 Remain Finally (and it is in the spinal 

 ganglia of the smaller mammalian animals 

 that we obtain the most characteristic 

 objects), isolated apolar cells are to be 

 found (t), probably but undeveloped forms 

 of the first kinds. It appears, neverthe- 

 less, undeniable that a certain number of 

 the nerve-tubes entering the spinal gan- 

 glia may pass through the latter without 

 being connected in the least with its 

 cells. How many do so is not yet deter- 

 mined. 



The ganglion cells found in the sympathetic knots (fig. 320, d, ,/) 

 appear to be somewhat smaller as a rule, but not so much so that we 

 should feel ourselves justified in placing a distinction between sympathetic 

 cells and cerebro-spinal on this account. 



tn^YT^ 8 fib eS are S me of them broad > but for the most part fine 

 es (a, b C ). Besides these, there may be seen in the sympathetic 

 ganglia, and sometimes in considerable quantity those formations known 

 as Ucmaks fibres 



Finally, turning to the relation of the two kinds of structural elements 



Fig. 319. A spinal ganglion from the 

 mammal c (diagrammatic), a, anterior 

 or motor, 6, posterior or sensitive root ; 

 , , efferent nervous trunk; *, direct 

 and I, tortuous fibres; / unipolar, g 

 and A, bipolar, and t, apolar ganglion 

 ceils. 



