08 



MUSCULAE TISSUE 



lighter disk, or intermediate disk of Krause, is commonly designated by 

 the letter J (Isotrope streife) ; the dark disk, or transverse disk of 

 Briicke, by the letter Q (Querscheibe). On closer inspection the J 



disk is seen to be bisected by a 

 dark disk or membrane, the 

 ground membrane of Krause. 

 designated by the letter Z 

 (Zwischenscheibe) . Indeed 

 this is the most conspicuous 

 stripe, and gives to the mus- 

 uc cle, as seen under ordinary 

 low magnification, its band- 

 ed appearance in uncontracted 

 fibers. The term teloi>ln-it<nna 

 has recently been employed by 



FIG. 106. THE CENTRAL PORTION OF THE 

 PRECEDING FIGURE, MORE HIGHLY MAG- 

 NIFIED. 



o, intercalated disk; en, endothelial nuclei 

 of a capillary; Nuc, nucleus of muscle syn- 

 cytium. ' Hematein and eosin. X 500. 



Heidenhain for this mem- 

 brane. The myofibrils are in- 

 timately connected with it. 

 Similarly, the Q disk is bi- 

 sected by a narrow light disk, the median disk of Hensen (H), which in 

 turn is said to be bisected by the intermediate membrane of Heidenhain, 

 or meeophragma (M, Mittelscheibe). Both telo- and mesophragmata 

 (inophragmata) are supposed to unite with the sarcolemma peripherally, 

 and to be structurally similar. The telophragma is in intimate connec- 

 tion both with the sarcolemma 



and the nuclear membrane. But ^^ 



the mesophragma, at least in (J- W 



striped muscle of certain forms, A 



e.g., Limulus, is not a true A 



membrane to which the fibrils 



are attached in the manner of 



the telophragma. Indeed it re- 4 % 1 



mains an open question whether ^ 



heart muscle actually possesses 

 a mesophragma. 



The portions of a fibril, or 

 sarcostyle, included between 

 successive telophragmata, con- 

 stitute structural units, the sar- 

 comeres, or inokommata (Heidenhain, Fig. 110). In macerating fluids 



FIG. 107. TRANSECTION OF A GROUP OF 

 CARDIAC- MUSTLE FIBERS FROM A PAPIL- 

 LARY MUSCLE OF THE HUMAN HEART. 

 Hematein and eosin. X 550. 



