NERVES. Ml 



from the circumstance of their frequently exhibiting no trace 

 of longitudinal striae, 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. Hound 

 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 striae 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 : 1st, fibres, nervous fibres in the ex- 



