96 



GENERAL ANATOMY OF THE TISSUES. 



/ £§86 





Fig. 38. ganglion-cells or ganglion-globules , are 



/' endowed with the common attributes of 

 £ cells. Their membrane presents no 

 peculiarity, except that, frequently, it 

 is very delicate, and even, as in the 

 great central masses, eventually perhaps 

 wholly disappears. The contents are 

 finely granulated, semi-solid, often con- 

 tain pigment, and without exception in- 

 close a distinct vesicular nucleus with a 

 large nucleolus. In size, the nerve-cells 

 vary from 0*003 — 004'", and as regards 

 their form, they may be distinguished 

 principally into round, fusiform, and 

 stellate. The two latter kinds are 

 produced by the prolongation of many 

 nerve-cells into two, three, to eight and 

 more, processes, which in some cases, 

 after a short course, pass into medullated 

 nerve-fibres, in others, present a more 

 marked independence, since, preserving a complete resemblance 

 to non-medullated nerves, they often run for a considerable 

 distance, and branch out in manifold ways. In what manner 

 finally these processes end, whether free or in connection with 

 nerve-tubules or by anastomosis with similar processes, is not 

 yet made out ; though, upon the whole, it would seem to be not 

 improbable that all three possibilities may occur in different 

 localities. 



Nerve-fibres and nerve-cells are combined iuto two sub- 

 stances, which in extreme cases present very wide differences, 

 the grey and the white substances. The former constitutes the 

 so-called white medulla or medullary substance of the spinal 

 cord and brain, and the nerves ; it consists essentially of nerve- 

 tubules, united into bundles or interwoven into plexuses, with 

 blood-vessels ; added to which, in the peripheral nerves, we 

 have special investments of connective tissue, the so-called 



Fig. 38. Nerve-cell of the Pike (so-called bipolar), passing at its two ends into 

 dark-bordered nervous tubules, treated with arsenious acid, x 350 : a, membrane of 

 the cell; b, nerve-sheaths ; c, medulla of the nerve; d, axis-fibres connected with 

 the contents of the nerve-cell ; e, retracted from the membrane. 



