140 MUSCLE. 
tive fibres (fibrils) of muscle. These longitudinal fibres do not 
appear to represent the original condition of the secondary 
deposit, but the latter is structureless at first, and its trans- 
formation into fibres takes place subsequently. The change 
seems, however, to commence at a very early period, and 
indeed before the cavity is completely filled. The transverse 
strie of the muscular fasciculi, which, according to my mode of 
explanation, are produced by the peculiar form of the primitive 
fibres, likewise make their appearance before the complete 
filling up of the cell-cavity, as pl. IV, fig. 3, c, exhibits. 
According to the observations of Meyen on the formation 
of the cells of the liber, after the coalescence of the cells and 
absorption of the septa, a secondary deposit also takes place 
upon the common cell-membrane in the same way that we 
have observed to take place in muscle; but I know of nothing 
amongst vegetables analogous to a secondary deposit consisting 
of longitudinal fibres. On the contrary, according to Valentin, 
such deposits appear to take place in plants universally in 
spiral lines. The beaded appearance which the primitive mus- 
cular fibres here and there present, might perhaps be regarded 
as the result of this tendency to a spiral formation, the intu- 
mescences (beads) being so placed, as to produce the transverse 
strie, and the latter may perhaps be spiral and not circular. 
This is, however, a mere conjecture, and requires further re- 
search. 
The involuntary muscles, such as do not present the trans- 
verse striz, appear to originate in a manner similar to that 
just described. They differ, however, from the voluntary or 
striated muscles, in their fibres being generally shorter than 
those of the latter; probably, therefore, fewer primary cells 
arrange themselves together to form a secondary cell, and 
their fibres are commonly thinner and flat. I found im a 
human uterus, which contained a mature foetus, some long 
muscular fibres of the breadth of the common primitive fasci- 
culi of voluntary muscles, which were so flat as scarcely to 
amount to 0:0010 to 0:0015 of a line in thickness. The 
involuntary muscles, likewise, have cell-nuclei, proving that 
the fibres composing them do not correspond to the primitive 
fibres (fibrils), but to the primitive fasciculi of the voluntary 
muscles. An opposite view of the matter might be taken 
