32 NERVOUS SYSTEM. 



than the primitive nerve-tubes, but they preserve even tc 

 the terminal extremity their double contour, and there can 

 be demonstrated, very easily, a sheath provided with nuclei, 

 a medullary layer, and the axis-cylinder. Never do we ob- 

 serve at the termination of the motor nerves the pale and 

 non-medullated fibres described by Kuhne and Kolliker. 

 At the point where the tube terminates, we remark con- 

 stantly a special arrangement which has no analogy with 

 that which has been described in the batrachia by these two 

 observers, and which Kuhne believed could be extended to 

 the higher vertebrata, to the mammalia, and to the human 

 subject. The nerve-tube, with a double contour, preserving 

 still a diameter of from -g^-^ to -g^Vir f an mcn a * ^he point 

 where it touches the primitive fasciculus to become arrested 

 at its surface, terminates by an expansion of the central 

 nerve-substance, the axis-cylinder, which is in immediate 

 contact with the contractile fibres (fibrillse) of the primitive 

 fasciculus. The layer of medullary substance ceases ab- 

 ruptly at this point, the sheath of the tube is spread out and 

 blended with the sarcolemma ; but in immediate continuity 

 with the axis-cylinder, a layer, a plate of granular substance, 

 from -g-jnnr to ^-g-j-o ^ an mcn m thickness, is spread out be- 

 neath the sarcolemma, on the surface of the fibrillse, in a space 

 generally oval and about y^Vo f an mcn wide in its short 

 diameter, and -g-J-^- of 3n inch in its long diameter. This 

 granular substance masks more or less completely, in the 

 space which corresponds to it, the transverse strige of the 

 muscular fasciculus. The disk itself has exactly the granu- 

 lar appearance of the substance of the axis-cylinder in the 

 vertebrata, and of that of the nerve-tubes in most of the inver- 

 tebrata, especially after being treated by diluted acids. But 

 that which essentially characterizes the terminal plates of the 

 motor nerves is an agglomeration of nuclei observed at 

 their site. "With a low magnifying power, even, we can dis- 

 tinguish the point where a nerve-tube touches the primi- 

 tive fasciculus to which it belongs, and ends abruptly at its 



