. A treatise on nervous and mental diseases, for students and practitioners of medicine. nkle-clonus. Bladder and rectal centres. The axis-cyliuder occupies the central part of the fully formednerve (Fig. 47). It is a grayish strip, having very faint, even out-lines on each side. Surrounding the axis-cylinder is a substanceof a fatty nature, vvhich is called the medullary sheath. Themedullary sheath is in segments, as was shown by the French , Ranvier. The breaks by these segments in the coutiuuity<jf the medullary sheaths are known as the constrictions of axis-cyli
. A treatise on nervous and mental diseases, for students and practitioners of medicine. nkle-clonus. Bladder and rectal centres. The axis-cyliuder occupies the central part of the fully formednerve (Fig. 47). It is a grayish strip, having very faint, even out-lines on each side. Surrounding the axis-cylinder is a substanceof a fatty nature, vvhich is called the medullary sheath. Themedullary sheath is in segments, as was shown by the French , Ranvier. The breaks by these segments in the coutiuuity<jf the medullary sheaths are known as the constrictions of axis-cylinder can be seen passing across from one to the otherof these segments. Upon exposure the medullary sheath undergoes 6 66 INTRODUCTORY, a sort of coagulation and strongly refracts the light, giving rise oneither side to dark contours which pursue the same sinuous peculiar markings have been observed in the medullarv sheath,and designated as the arrow markings, or incisures of Schmidt, Ixit itis not certain that they are not artificial products. Surrounding the Fig, Drawing of nerve. Obtained by teasing. medullary sheath and the contained axis-cylinder is a fine transparentconnective-tissue substance, ensheathing the medullary substance andaxis-cylinder like the finger of a glove, and known as the sheath ofSchwann, being named after the anatomist of this name. Nuclei aresparsely distributed along it. Some nerve fibres, especially in thesympathetic nervous system, have no medullary sheath, but thesheath of Schwann immediately surrounds the axis-cylinder; and thisdifference has occasioned a classification of nerve fibres into themedullated and non-medullated. The medullated fibres are gener-ally found everywhere but in the sympathetic nervous system. Inthe central nervous organs the sheath of Schwann is absent, whilstit is always present in the peripheral nerves. In entering the ter-minal structures in the motor and sensory tissues the medullatedfibres lose the
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