ORIGINAL COMMUNICATIONS. 
On the DeveLopmMENT of Strirpep MuscuLar Fisre in Man, 
Mammatta, and Birps. By J. Locxnart Crarxg, F.R.S. 
(Continued from page 231, vol. ii.) 
On the Development of Muscular Fibre in Man. 
In man the development of striped muscular fibre is on 
the same plan as in birds and mammalia, but presents some 
points of difference that deserve consideration. In its early 
stage one does not observe those striking forms that appear 
in the chick between the sixth and seventh days of incuba- 
tion (Pl. XI, fig. 9), and in the sheep or ox at a correspond. 
ing period. From the fourth to the fifth week of utero- 
gestation is about the earliest period at which this tissue can 
be distinguished with certainty from some others. Ina foetus 
of three fourths of an inch in length it forms a gelatinous 
mass, consisting, as in the other cases described, of fibres 
and nuclei imbedded in a semifluid, granular blastema. 
Pl. I, fig. 18 represents fibres from a foetus three fourths 
of an inch in length; and fig. 19 both fibres and free 
nuclei from another foetus, of one inch in length. In the 
formation of these fibres, as in similar cases already de- 
scribed, granular processes of condensed blastema extend 
from the sides or from around the nuclei; and along the 
surface of these a new substance forms, until they become 
partially or completely invested. At first the investing 
substance appears only on one side, in the form generally of 
a plain band or fibre (see fig. 18 a), but subsequently is seen 
also on the other. Sometimes, however, it is deposited in 
the shape of distinct, longitudinal fibrille, until the surface is 
completely covered (fig. 18 4); and sometimes these fibrillze 
are at once or soon after divided into particles, which, when 
close together and on the same level, appear as transverse 
strie (fig. 18d). Seen under a power of 420 diameters, 
these two rows of particles had the appearance of short, trans- 
verse lines. On one side of them are the remains of the 
granular layer of blastema, ready to be converted into 
VOL, III.—NEW SER. A 
