288 



MUSCULAR TISSUE. 



to them, for it is seen in the fibres of the heart, and striped fibres are also found 

 in some other viscera, such as the pharynx and upper part of the gullet. 



When the muscular fibres are deeply f ocussed, the appearance of the striae becomes some- 

 what altered, and a fine line, often dotted, is seen passing across the middle of each light band, 

 (see fig. 328). This has been termed Dalle's line or the stria of Amid ((Usque wince, Zun- 

 xcliemclteibe'), and it has been supposed to represent a membrane stretching across the fibre and 

 attached at the surface to the sarcolemma (see below). The line is, however, not visible in the 

 most superficial planes of the fibre, and although there certainly are membranes crossing the 

 fibre at about this situation, they are only seen when the fibre is treated with acids and certain 

 other reagents. There is reason to believe that the appearance of a dotted line in this situation- 

 in the fresh fibre is due to the peculiar optical conditions of the tissue. 



A fine clear line is sometimes to be seen in the middle of each dark band. This was first/ 

 noticed by Hensen, and named the line or disk of Ilcnsen. 



Fig. 327. MUSCULAR FIBRE OP A MAMMAL EXAMINED FRESH IN SERUM, HIGHLY MAGNIFIED. (E. A. S.) 



This figure was drawn with the surface layer of muscular substance accurately focussed, the lateral 

 portions having been added by gradually sinking the focus. 



The nuclei are seen on the flat at the surface of the fibre, and in profile at the edges. 



Fig. 328. PORTION OF A HUMAN MUSCULAR FIBRE SHOWING DOBIE'S LINE IN THE MIDDLE OF 

 THE CLEAR BAND. (Sharpey. ) 



The proper substance of the fibre presents, besides the transverse bands, an 

 appearance of longitudinal striation. On separating the fibre with needles, especially" 

 after hardening in alcohol, it may be broken up longitudinally into fine longitudinal 

 elements, of a rounded or angular section, which run from end to end of the fibre ? 

 these may be conveniently termed muscle-columns (Kolliker) or sarcostyles. 1 Each 

 sarcostyle appears to consist of a row of elongated prismatic particles with clear 

 intervals. These particles may be termed sarcous elements (Bowman). The 

 sarcostyles are united into the fibre by a variable amount of intercolumnar substance 

 to which the name sarcoplasm has been given (Rollett). In some muscles the sarco- 

 styles can be made out to be longitudinally striated, an appearance which has led 

 some authors to believe that they are composed of still finer elements or fibrils, 

 a term which has also been employed to denote the muscle-columns themselves. 



Under certain circumstances the fibres show a tendency to cleave across in 

 a direction parallel to the bands, and even to break up into transverse plates or 



1 <rop|, muscle ; arvKos, a column. 



