RESTORATION OF CO-ORDINATED MOVEMENTS AFTER NERVE SECTION. 697 



sheath of Schwann, having at intervals spindle-shaped nuclei encroaching on the 

 medullated sheath. Such fibres are, however, very much smaller than the medullated 

 nerve fibres of the central segment. Many other fibres are present, which show less 

 distinct characters, and are finer, but in which the axis-cylinder is equally distinct, but 

 with less prominent medullated sheath ; while in other cases the axis-cylinder is so 

 indistinct as to be recognisable with difficulty, and only so in parts of the fibre, the 

 parts in which it is not recognisable looking very like connective tissue fibres. At this 

 level of the segment there are a few bulky leucocytes present, but no distinct remains 

 of the degenerated old fibres. In portions of the branches of this nerve from the 

 middle of the leg the most striking difference is that there are present remains of the 

 degenerated old fibres — balls of myelin arranged in columns one behind the other, 

 together with many leucocytes loaded with degeneration products. But between these 

 degeneration remains are present abundant young nerve fibres, either singly or in 

 bundles. 



In Exp. II. the peripheral segment presents also an abundant supply of young nerve 

 fibres, but being at the thirtieth day of development, the stage is not the same as in 

 Exp. L, which is at the fifty-fourth day of development. The essential differences are 

 that the young nerve fibres do not show the medullated sheath so distinctly as do the 

 furthest advanced fibres in Exp. I., and that degeneration remains are still present close 

 to the seat of reunion, lying between the young fibres, while in the sections prepared 

 from the terminal divisions of the nerve the degeneration remains are still more 

 abundantly present, with the young fibres still finer and less distinct. 



In Exp. III., at the forty-ninth day of development, the young nerve fibres are 

 not quite so far advanced as in Exp. L, and some distinct remains of old degenerated 

 fibres are still present, not only in the terminal divisions of the nerve, but also close to 

 the seat of reunion. 



The Nerve Cicatrices (Plate II. figs. 2 and 3). — The appearances presented in each 

 of the three cases show no important differences. The fasciculi of the central and 

 peripheral segments pass into the cicatrix, the nerve fibres diverging to some extent, 

 the fibres of the central segment being, as in the peripheral segment, in every case new- 

 formed fibres. The continuity of these fibres across the cicatrix is not traceable, although 

 at some points, especially in the sections from Exp. I., it is clear that the fibres do in 

 reality pass right across, but that they are not traceable simply from the fact that they 

 pass out of the plane of the section. This is shown in the middle line of the section, in 

 which fibres may be traced for a considerable distance, until they suddenly terminate, 

 their further course being contained in other sections of the series. But fibres which 

 for some distance have run parallel, but which drop out of the section when traced 

 centralwards, continue their course into the peripheral segment. In the greater part of 

 the cicatrix the fibres evidently run a very tortuous course, as they are seen in the 

 sections cut in all directions, some showing for short distances in longitudinal section, 

 while others appear as small clusters of transversely cut fibres. The entire cicatrix has 



