MODE OF TERMINATION OF MOTOE NERVES IN AMPHIBIA. 213 



if the nerve has been forcibly stretched at the point where it 

 appears to be most easily torn, does the medullary portion re- 

 tract, so that a small empty funnel hangs over the border of 

 the muscular fibre. Beneath the sarcolemma the nerves, now 

 destitute of medullary sheaths, may be recognised in the form 

 of small, moderately broad fibres, extending in a direction 

 parallel to the muscular fibres, and often somewhat exceeding 

 the breadth of the finest medullated branches. These fibres form 

 a delicate pattern between the contractile substance and the 

 sarcolemma, dividing and giving off branches of nearly equal 

 breadth, from which again others course in a nearly parallel 

 direction. The whole system which they form is usually three 

 or four times longer than the transverse diameter of the muscular 

 fibre. It never invests the whole circumference of the contractile 

 substance, and the branches never penetrate far into the interior 

 of it. There can be no question that we have here an intra-muscu- 

 lar branched expansion of the axis cylinder, and that it is the 

 axial portion of the doubly contoured nerves which alone pene- 

 trates the sarcolemma, and forms beneath it a wide-meshed 

 and in part fibrillated plexus. The fibres of the plexus appear 

 to be in part round and partly flattened ; they are very trans- 

 parent, with delicate and for the most part smooth, though 

 here and there finely serrated, contours. 



Good instruments show with sufficient sharpness that the 

 intra-muscular axis cylinders are not diffusely troubled or 

 granular at their terminations. The actual extremity is 

 always a distinctly rounded point. Here and there the axis 

 cylinders are somewhat enlarged, and in such places small 

 strongly granular corpuscles may usually be observed, the size 

 of which is intermediate between those of the nuclei in the 

 sheath of Schwann and the well-known muscle nuclei. They 

 are pear-shaped, with the pointed extremity directed towards 

 the end of the axis cylinder, and are found not only in the 

 expanded portions of the latter, but occasionally in other parts, 

 though always lying close to the axis cylinder. The finer 

 structure of these terminal nerve bulbs may be well seen even 

 with ordinary microscopic powers, but still better with a very 

 strong objective and a low ocular. A fine tortuous fibre may 

 then be observed to separate from the axis cylinder, which in 



