4 CLARKE, ON STRIPED MUSCULAR FIBRE. 
presented at a, 6, fig. 20, in which, particularly, in a, if we 
suppose a number of other fibrille of the same kind to be 
deposited round the nucleus a’ and its granular prolongations, 
we should have a general resemblance to the fibre now under 
consideration, in which it was easy to see, by changing the 
focus, that the whole of its upper surface consisted of fibrille 
similar to those at its sides. When the granular axis has 
disappeared, and the fibre throughout is composed of fibrillze, 
and is therefore of uniform structure, the lateral bands, as 
bands, of course, disappear; while the nuclei, in many in- 
stances, reach the surface, in consequence of the unequal 
deposition of material around them. In other cases, how- 
ever, the nuclei have seemed to disappear by breaking up 
into granules; but I am not sure that this is a natural histo- 
logical change. In the embryo of the fowl, when the fibres are 
changing from the condition represented at a, fig. 12, to that at 
a, fig. 13 (Pl. XI)—that is, when the axis is disappearing, and 
the fibre is becoming a compact bundle of fibrillae—the nuclei 
seemed as if they were escaping to the surface between the 
fibrillee, as it were, by pressure, for many of them were partly 
between and partly without the fibrille. I have not wit- 
nessed the same appearances in mammalia, nor have I seen 
the same reed-like structure of the fibres as is represented at 
a, fig. 12, where the nuclei seem as if they were compressed 
by the lateral bands stretched over them at intervals. 
Up to the time of birth nothing of importance remains to 
be observed. Fig. 23, Pl. I, represents three muscular fibres 
from the leg of a human feetus of three and a half months; 
one of them is left blank. 
Such are the results of my own observations on the deve- 
lopment of striated muscular fibre. Let us now consider 
how far they agree with the theories and observations of pre- 
vious inquirers. 
It is well known that, according to Schwann, every mus- 
cular fibre is at first developed from round nuclear cells, 
which arrange themselves in linear series and coalesce at 
their pomts of contact. The septa by which they are sepa- 
rated then become absorbed, so that there results a hollow 
cylinder,—the secondary cell of muscle, within which the 
nuclei of the original cells are contained, generally lying 
near together on its wall.* 
In 1849-50 Lebert published some investigations on the 
development of the same tissue in vertebrate animals,t+ 
opposing at the same time the theory of Schwann. Spcak- 
* * Microscopical Researches,’ &c., p, 141. 
+ ‘Annales des Sciences naturelles.’ 
