JOURNAL OF MICROSCOPICAL SCIENCE. 
DESCRIPTION OF PLATE I, 
Illustrating Mr. J. Lockhart Clarke’s paper on the Develop- 
ment of Striped Muscular Fibre in Man, Mammalia, and 
Birds. 
Fig. 
18.—Muscular and nerve-fibres from the trunk of a human feetus of six 
weeks: @ are two fibres from the thigh in process of formation, 
magnified 670 diameters. In the lower one two oval nuclei are 
united by granular processes proceeding from one of their ends ; 
similar processes extend from their other ends; along one side 
of the nuclei and processes a thick fibre or lateral band is laid 
down ; in the upper fibre a border is formed on both sides, but. is 
much finer on one side. 4 Is another fibre from the same region, 
magnified 900 diameters ; it is in different. states of development 
at different parts, and is an object of great interest. On one side 
of the nucleus, at c, there are two distinct but smooth borders,and 
between these the surface of the fibre, as well as of the nucleus, 
shows indications of longitudinal, but simple or unresolved, 
fibrille. On the opposite side of the nucleus, at d, the lower 
border or band, as well as one of the fibrillee on the surface, has 
already become resolved into sarcous elements, but the wpper bor- 
der, except near the nucleus, has not yet been laid down, and the 
edge of the fibre is somewhat ragged, with granular blastema, 
which may be also seen between and beneath the fibrille and 
sarcous elements deposited upon it. e Are four delicate nerve- 
fibres from the same region of the same fetus. 
19.—Muscular fibres and free nuclei from the leg of a human fcetus of two 
months, magnified 420 diameters. 
20.—Fibres from the same, magnified 670 diameters: a is a striated fibre, 
consisting of at least two fibrille; along one of its sides a nucleus 
and a layer of blastema have been laid, upon which new fibrille 
are to be laid down. J& Is another fibre, in which the two fibrillee 
composing it are more distinctly seen; nuclei with granular pro- 
cesses are seen along its edge; at ¢ part of the lateral bands have 
become resolved into sarcous elements. 
21.—Represents muscular fibres and free nuclei from the ventricles of 
the heart of a human fetus 2 inch long, magnified 420 dia- 
meters: a, free nuclei of different kinds; 4, nuclei zm situ, with 
granular processes and fibres; c, different kinds of fibres; d, a 
fibrilla with fine branches resolved into sarcous elements; e, fibres 
collected into a bundle; at fthe striations are seen. 
