NERVES. 141 
from the circumstance of their frequently exhibiting no trace 
of longitudinal striz, and that probably the greater portion of 
them do not contain other more minute primitive fibres, or 
at least only such as are imperfectly developed. In this re- 
spect they are not so highly developed as the voluntary 
muscles. Perhaps the peculiar secondary deposit upon the 
cell-membrane of the secondary cell is all that is essential to 
the contraction of muscle; and it may not be important that 
that substance should consist of minute longitudinal fibres. 
In order briefly to recapitulate our researches into the 
generation of muscle, the process may be thus stated. Round 
cells, furnished with a flat nucleus, are first present, the 
primary cells of muscle. These arrange themselves close 
together in a linear series; the cells thus arranged in rows, 
coalesce with one another at their points of contact ; the septa, 
by which the different cell-cavities are separated, then become 
absorbed, and thus a hollow cylinder, closed at its extremities, 
the secondary cell of muscle, is formed, within which the 
nuclei of the original cells, from which the secondary cell has 
been formed, are contained, generally lying near together on 
its wall. This secondary cell, then, passes through all the stages 
of a simple one. It expands throughout its entire length, 
whereby the nuclei are farther removed from one another, 
and sometimes even become elongated in the same direction. 
A deposit of a peculiar substance, the proper muscular sub- 
stance, takes place at the same time upon the inner surface 
of the cylinder, by which the cavity is at first narrowed, and 
at length completely filled. The cell-nuclei lie external to this 
substance, between it and the cell-membrane of the secondary 
cell. 
The transverse striz in the voluntary muscles become more 
manifest, and the deposited substance is more distinctly seen 
to be composed of longitudinal fibres, as the foetus advances 
in age. ‘The nuclei are gradually absorbed. The cell-mem- 
brane of the secondary muscle-cell remains persistent through- 
out life, so that each primitive muscular fasciculus is always to 
be regarded as a cell. 
2. Nerves. The nervous system presents two forms of 
elementary structure: Ist, fibres, nervous fibres in the ex- 
