. Text-book of normal histology: including an account of the development of the tissues and of the organs. the pial septa, as well as intermingle with Fig. 320. the nerve-fibres ; amongthe latter lie the charac-teristic spider-cells,sending their long, deli-cate processes betweenthe fibres. The white matter ofthe cord is made up seem-ingly of great numbers ofsmall round nucleated ele-ments, held together bythe supporting apparent cells arethe nerve - fibres intransverse section, the supposed nuclei being really the cut axis-cylinders ; an irregularlyconcentric striation is usua
. Text-book of normal histology: including an account of the development of the tissues and of the organs. the pial septa, as well as intermingle with Fig. 320. the nerve-fibres ; amongthe latter lie the charac-teristic spider-cells,sending their long, deli-cate processes betweenthe fibres. The white matter ofthe cord is made up seem-ingly of great numbers ofsmall round nucleated ele-ments, held together bythe supporting apparent cells arethe nerve - fibres intransverse section, the supposed nuclei being really the cut axis-cylinders ; an irregularlyconcentric striation is usually present around the axis-cylinder, thisappearance being produced by the partial distortion of the medullarysubstance. The nerve-fibres of the cerebro-spinal axis possess noneurilemma, the surrounding neuroglia affording the necessaryprotection. The individual nerve-fibres composing the white matter of thecord vary greatly in diameter (1-27 //) ; while the thick and the thmfibres are found side by side in all regions of the cord, certaincolumns are characterized by the predominance of thick Portion of white matter of human spinal cord : a, largenerve-fibres in section; b, smaller fibres; c, supportingneuroglia; d, spider-cell; e, connective-tissue trabeculacontaining blood-vessel,/; g, spaces from which sectionsof nerve-fibres have been lost. 288 NORMAL HISTOLOGY. Fig. 321. while other tracts contain mostly small ones. With reservation, itmay be assumed that motor fibres are generally the largest (15-20 m): hence the nerves issuing from the anterior cornua containprincipally fibres of large size ; the posterior sensory nerves andthe sensory tracts, on the contrary, contain chiefly small fibres,although a number of fibres of large diameter are usually largest fibres occur within the direct and crossed pyramidaltracts ; the smallest, within the column of GoU. The white commissure in man forms a continuous nervouslamella, .3-5 mm. in thickness, which separat
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