MUSCULAR TISSUE. 



are little masses of pellucid substance presenting a rectangular outline, 

 and appearing dark in the centre. Their appearance, indeed, suggests the 

 notion of minute vesicular bodies or cells, cohering in a linear series, the 

 faint transverse marks between being the lines of junction." * On altering 

 the focus, however, the dark spot, as Dr. Sharpey continues to observe, be- 

 comes light and appears transparent, though less so than the bright mar- 

 ginal portion. Moreover, when very highly magnified, the dark central 

 part also appears, according to the same observer, marked or constricted in 

 the middle, as if consisting of two separate particles. Whether, therefore, 

 the appearances above described depend on each pellucid particle being 

 really a nucleated cell, and whether the ultimate fibril is to be considered 

 as composed of a single row of such cells opposed end to end, by whose 

 closer approximation to each other the contraction of the fibril is effected, 

 are questions not yet determined. 



After repeated examinations of transverse sections of striped muscular 

 fibre, M. Stadelmann f has convinced himself that (as was stated by Mr. 

 Bowman) J the tube of the primitive fibre is invariably filled throughout 

 with fibrillse, and never presents the central cavity described by some 

 writers. A slight appearance of the existence of such cavity is frequently 

 afforded by the dots, which indicate the cut fibrillse, being much paler at 

 the centre of the fibre than towards its circumference, but they are never 

 so pale as to be invisible. 



Came of the striped appearance of animal muscular fibre. In addition 

 to the several arguments employed by Professor Miiller, in favour 

 of the opinion that the tranversely striated appearance of voluntary 

 muscular fibre is due to the peculiar structure of the ultimate fibrils of 

 which the fibre is composed, and not to markings on the sheath of the fibre, 

 Mr. Bowman draws attention to another conclusive circumstance, namely, 

 that by successively bringing into focus fresh portions of the depth of a 

 fibre, the first observed stria} become confused, or even vanish, whilst others 

 come into view ; shewing that they exist not merely on the surface, but 

 through the entire thickness of the transparent fibres. || 



Relative size of the fibres and fibrils of striped muscle in the foetus and 

 adult. The correctness of Mr. Skey's statement, IF that the primitive 

 fibres of voluntary muscle in the foetus have a diameter about one- 

 third of that which they possess in adult age, has been recently shewn 



* Dr. Sharpey, 1. c. p. clxviii. 



t Reichert's Bericht in Miiller's Archiv. 1845, p. 192. 



J Philosoph. Trans. 1840, p. 467. Miiller's Physiology, p. 880. 



|| Philosophical Transactions, 1840, p. 468. The two Webers remain the strongest 

 upholders of the opinion that the transverse markings of the fibres are seated in the 

 sheath ; but since their evidence in favour of this view is by no means conclusive, it is not 

 necessary to do more than refer to the article " Muskelbewegung " in Wagner's Handwb'rter- 

 buch, by Professor Ed. Weber. f Muller P ysiology, p. 881. 



