110 



GENERAL ANATOMY OF THE TISSUES. 



pigment, and without exception enclose a distinct vesicular nucleus with 

 a large nucleolus. In size, the nerve-cells vary from 0'003-0-04 of a 

 line, and as regards their form, they may be distinguished principally 



Fig. 37. 



Fig. oS 



a..J, 



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, pro- 

 cesses, 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 con- 

 nection with nerve-tubules or by anastomosis with similar processes, is 

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

 probable that all three possibilities may occur in different localities. 



Nerve-fibres and nerve-cells are combined into two substances, which in 

 extreme cases present very wide differences, the gray and the white sub- 

 stances. The former constitutes the so-called white medulla or medullary 

 substance of the spinal cord and brain, and the nerves ; it consists essen- 

 tially of nerve tubules, united into bundles or interwoven into plexuses, 

 with bloodvessels ; added to which, in the peripheral nerves, we have 



Fig. 37. Tubular nerve-fibres of man. Four of them fine, two of tliem being varicose, 



one of a medium thickness with a simple contour, and four thick ones; two having double 

 contours, and two with granular contents. — Magnified 350 diameters. 



Fig. 3S. — Nerve-cell of the Pike (so-called bipolar), passing at its two ends into dark-bor- 

 dered nervous tubules, treated with arsenious acid: «, membrane of the cell; fc, nerve- 

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

 cell; e, retracted from the membrane. — Magnified 300 diameters. 



