INTERCALATED DISCS OF HEART MUSCLE 



159 



3. Guinea-pig 



Fig. 9 illustrates the typical condition in adult guinea-pig. 

 The discs are again aggregated in more or less definite areas; 

 they may be wide or narrow, delicate or robust, compact or loosely 

 granular. At the left, two discs are shown connected by a row 

 of granules; a similar disc, of mono-serial coarse granules, ex- 

 tends uninterruptedly across the two middle fibers. The same 

 condition, producing the disc-structure, prevails at approxi- 



Fig. 9 Section of guinea-pig heart muscle illustrating the several types of 

 discs, and their relation to each other, the fibrillae and the darker bands. 



mately the same level in the four adjacent fibers; the appearance 

 is incompatible with a cement line. Fig. 10 shows a disc of 

 three 'steps' and two 'risers' extending across a nucleus. Fig. 



11 illustrates a patch of compact and pale granular discs. Fig. 



12 shows a variation occasionally met with in the guinea-pig and 

 other mammals. Such a disc has not the remotest resemblance 

 to a cement line or to an intercellular Bridge. The thickenings 



THE AMERICAN - JOURNAL OF ANATOMY, VOL. 13, NO. 2 



