PLATE X1—(continued). 
Fig. 
13.—Muscular and nerve-fibres from leg of chick on the fifteenth day of ineuba- 
tion: a, a large muscular fibre ; its upper and lower parts represent the 
different states of the fibrille in different fibres or in different parts of the 
same fibre; two nuclei are cemented to its side by a layer of blastema. 
&. A smaller muscular fibre, with the fibrillae here and there divided into 
sarcous elements ; numerous nuclei are attached alternately round its sur- 
face. c. Three nerve-fibres from the leg. 
14.—Muscular fibres and nuclei from the back of a foetal sheep # inch in length, 
maguified 420 diameters: @ represents the appearance of the fibres and 
nuclei in their normal position; 4 are finer fibres connected with nuclei 
and with the thicker fibres, as atc. d Is one of the thicker fibres, isolated 
from the rest; it is formed along the sides, or rather by the coalesced ends 
of a series of pyriform, imbricate nuclei; a branch of the fibre is formed 
along the surface of the uppermost nucleus. d, e, fg, f, t, 7, 7, Are other 
fibres of the same kind, formed along masses of blastema variously connected 
with nuclei. 
15.—Part of a large muscular fibre from the trunk of a foetal sheep two inches in 
length, magnified 420 diameters: the axis enclosed by the lateral bands 
contains numerous nuclei, and a delicate, granular blastema. 
16.—Muscular fibres, in different states of development, from the leg of a foetal 
ox five inches long, magnified 420 diameters: the period of utero-gestation 
appeared to be nearly the same as in the case of the foetal sheep two inches 
long. a. A small fibre in an early state of development; the nuclei, which 
occur in pairs, appear to be undergoing division. 4. A broader fibre, with 
nuclei bulging the surface, but of uniform structure, without lateral bands ; 
ec, another of a larger kind, with distinct axis and lateral bands; d, several 
small fibres closely applied to each other to forma bundle. Ate one end 
of a fibre has a granular axis, with large, nearly round nuclei, and distinct 
lateral bands; in the middle the fibre is much narrower and uniform in 
structure, like those at @ and 4, with much smaller and oval nuclei; at its 
other end the fibre again becomes broader, but retains the same uniform 
structure ; the nuclei are still oval, but much larger, and cause the fibre to 
bulge. / Is another fibre, presenting two different states of development ; 
at its lower part it is broader, and consists of distinct lateral borders, with 
granular axis and nuclei; its upper part, after having assumed a uniform 
structure with the nuclei at the surface, has become resolved into fibrille. 
g Is a fibre in which the border is much stronger on one side; 4, ¢, are 
two delicate fibres with scarcely any traces of lateral bands, and resembling 
the axes of larger fibres, possessing broad lateral bands; 7 is a large fibre, 
in which the constriction and change of structure have begun in the middle 
(j’); at each end there are distinct lateral bands, and a granular axis with 
nuclei; in the middle (7) the fibre has become narrower and assumed a 
uniform structure throughout its thickness, with the nuclei at the surface ; 
& is a large fibre, with thick lateral bands; its axis resembles the fibres ¢ 
and 4, without bands. 
17.—Transverse sections of muscular fibres from the leg of a fcetal sheep two 
inches long: at a a nucleus is nearly in the centre; at 4 it is on one side; 
at dand ¢ the granular axis is seen to be surrounded by the investing sub- 
stance, which is ultimately resolved into fibrille. 
