98 



MUSCULAR TISSUE 



a en 



FIG. 106. THE CENTRAL PORTION OP THE 

 PRECEDING FIGURE, MORE HIGHLY MAG- 

 NIFIED. 



a, intercalated disk; en, endothelial nuclei 

 of a capillary; Nuc, nucleus of muscle syn- 

 cytium. Hematein and eosin. X 500. 



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

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

 Briicker. 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- 

 Nuc cle, as seen under ordinary 

 low magnification, its band- 

 ed appearance in uncontracted 

 fillers. The term teloplirmima 

 has recently been employed by 

 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 mesophragma (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 

 striped muscle of certain forms, 

 e.g., Limulus, is not a true 

 membrane to which the fibrils 

 are attached in the manner of 

 the telophragma. Indeed it re- 

 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 uiokommaia (Heidenhain, Fig. 110). In macerating fluids 



FIG. 107. TRANSECTION OF A GROUP OF 

 CARDIAC MUSCLE FIBERS FROM A PAPIL- 

 LARY MUSCLE OF THE HUMAN HEART. 



Hematein and eosin. X 550. 



