378 
MR. SKEY ON MUSCULAR FIBRE. 
tracted, and are occasionally elongated even to a point. Frequently, however, the 
fibre retains its natural diameter up to its termination in the jagged circle (Plate XVII. 
fig. 1 . c.). This part of the fibre will occasionally exhibit an orifice, such as would appear 
by the foreshortening of a tube cut obliquely. When a section of the fibre is made 
in the vertical direction, this appearance is not observed. 
It is difficult to obtain a distinct view of the tubular end of a fibre by any careful 
preparation of the object, but ivithout such preparation several fibres in the same ob- 
ject, may exhibit its tubular character. If such a fibre be brought into focus at its 
extremity, the circular striae and longitudinal filaments will be exposed, extending to 
the near margin, and if the depth of the fibre be then penetrated by the microscope, 
the longitudinal filaments of the opposite side will be jirst exposed, and secondly, the 
circular striae, but neither of these will be distinct, being obscured by the glutinous 
lining of the interior of the tube. A careful adjustment will thus detect the aperture 
of the tube of the fibre, which appears in the form of a hollow cylinder, perfectly 
translucent in its centre, but less so at its sides from their vertical direction to the 
plane on which they rest. The latter present when in focus the dark outline of the 
fibre, extending along its length. 
If a single fibre be divided in the longitudinal direction its cavity may be exposed 
along a considerable length, the filaments composing the fibre with their investing- 
striae of the opposite side of the cylinder may then be seen when the near side is out 
of focus (Plate XVIII. fig. 1 . a.). 
As the tubular character of muscular fibre is not always distinctly apparent, I would 
add the following arguments in favour of this view of their composition. 
1st. A fibre is frequently elongated to a point, up to the extreme external surface 
of which, the circular strise are apparent. If the fibre be a solid cylinder, what be- 
comes of the central substance ? for it is evidently the external surface that is so atte- 
nuated, indicated by the presence of the circular striae. 
2nd. When a fibre is entirely separated into its filaments forming a fringe-like ex- 
tremity, that surface of the fibre nearest the eye, forms all that portion of the fringe 
which is distinctly in focus. If the focus be then changed the fringe of the opposite 
side is brought into view, but there is no middle fringe to complete what would then 
be, a solid tassel (Plate XVII. fig. 3.). 
3rd. If a few fibres be placed on glass and dried, little remains apparent, beyond 
the black outline of each fibre, their central portions become obliterated, and conse- 
quently the fibre is transparent. If the margin of the fibres are rendered dark by 
their perpendicularity to the plane below them, a fortiori, the middle portion of the 
fibre ought to exhibit the same phenomenon, for it is higher from the surface and 
consequently thicker. 
4th. The separation of a few or more filaments from the body of a fibre, never ex- 
hibits a second layer of filaments beneath them. This view of a central filament 
might reasonably be expected if each fibre were composed of a solid cylinder ; and 
