896 
PEOFESSOE BEALE ON THE DISTEIBTJTION OF NEEVES 
My specimens lead me to the conclusion that near the periphery the axis cylinder of a 
nerve-fibre cannot be distinguished as a separate structure from the white substance. 
The axis cylinder and the white substance seem to be, so to say, incorporated together 
to form the terminal part of the dark-bordered fibre. The dark-bordered nerve-fibre 
gradually becomes narrower as we approach its ultimate distribution, and it is resolved into 
several fine fibres ; but even in threads which are so fine as only to be scarcely visible the 
material appears to be of the same composition as the thicker parts of the fibre, and by 
the slow action of acetic acid globules of fatty matter are set free (Plate XLI. figs. 7, 8, 
& 9). I cannot but think that the very abrupt cessation, or sudden breaking off, of the 
white substance indicated in some of Kuhne’s drawings is due to the pressure of the thin 
glass upon the surface of the specimen, which renders comparatively large dark-bordered 
fibres quite invisible at the point where they cross the convexity of the muscular fibre. 
The white substance often diminishes in diameter rather abruptly, but it never ceases 
in the manner Kuhne has represented*; and I have never seen any appearances which 
lead me to conclude that the axis cylinder is prolonged independently of the white sub- 
stance ; nor do I think that “ here and there at least a thin layer of the white substance 
extends along the pale fibre,” as Kollikee remarks. 
The ultimate Distribution of the Werves in the Cutaneous Muscle from the Breast of the Frog. 
Let me now describe more particularly the results of my own observations on the 
ultimate distribution of the nerves to the muscular fibres of the frog. The fibres resulting 
from the division of the dark-bordered fibres, which to low powers appear terminal, are 
often seen to pass over the surface of a muscular fibre, and then become either suddenly 
attenuated, or gradually thinner as they cross in succession several elementary fibres of 
the muscle, or pursue a longitudinal course in the intervals between two fibres. In both 
cases they often give ofi* several branches. In the drawings of Kuhne the outline of the 
pale fibres is irregular, and their precise connexion with the dark-bordered fibre is not 
clearly indicated. In Plates XLII. & XLIII. figs. 11, 12, 13, 14, 15, & 17, it is seen that 
the dark-bordered fibre divides into two branches, and each branch may be followed for 
some distance as a definite but very narrow line (less than _i^th of an inch in dia- 
meter). This appearance is constant, and exists in every ‘ terminal ’ fibre. Nuclei are 
connected with these fine ‘ terminal ’ fibres, which are but the extension of the dark- 
bordered fibres ; and nuclei are also seen at intervals imbedded in the substance of the 
highly refracting matter of which the dark-bordered fibres are themselves composed. 
These nuclei are always to be found imbedded in the white substance near the finer 
divisions of the dark-bordered fibres (Plates XLI. -XLI V. figs. 8, 9, 11, 12, 14, 18, & 31). 
Around the fine fibres prolonged from the dark-bordered fibre, may be traced for some 
distance what appears to be the outline of the sheath (Plates XLII.&XLIII. figs. 13t&:16); 
* The thickness of the dark-bordered fibre just before it divides, as for example in the case of a fibre iu 
fig. 13, Plate XLII., is often increased by the shortening caused by the contracted state of the muscular 
fibre at the time of preparation. 
