INTERCALATED DISCS OF THE HEART OF BEEF 295 



the \e\v\ of focus from level 2 to kn^el 1 the discs in the upper 

 lighter region come into view. The latter are more delicate, 

 stain only relatively faintly and shade into the telophragmata. 

 This comjilex of discs may be interpreted in the light of the evi- 

 dence derived from the simpler conditions in figures 9 and 10. 

 The terraced disc probably formed along the oblique surface of 

 fusion of two distinct trabeculae. The band-discs in this re- 

 gion probably formed in connection with this same fusion as 

 incidental strain effects. 



Special note must also be taken of the alterations of the telo- 

 phi'agmata in this region. Accessory telophragmata appear to 

 pass obliquely between three successive primary teloplu'agmata. 

 The condition is probably the result of a rearrangement of the 

 telophragmata and subsequent fusion following a spiral twisting 

 of the fibers in this region. This group of discs no doubt suf- 

 fered a secondary alteration incidental to the spiral twisting. 

 The connecting accessory membranes between the three suc- 

 cessive telophragmata demonstrate the telophragma-nature of 

 certain of the 'risers' of the step-discs. 



The arrangement of the telophragmata in this trabecula dem- 

 onstrates, moreover, the possibility of a realinement of telo- 

 phragmata following gross morphological changes in the trabec- 

 ulae. It emphasizes also the imperative necessity, for a com- 

 plete interpretation of the intercalated discs, of dissociating the 

 fundamental structure, relation, and forms of the discs from their 

 secondary mechanical alterations follo^\ing distortion in the 

 trabeculae. 



Figure 14 shows an unusually large number of discs within a 

 relatively small area. The discs lie at different levels as indi- 

 cated by the numerals. The majority shade laterally into telo- 

 phragmata. Such an area would seem to defy interpretation in 

 terms of intercellular cement, tendons, coordination mechanisms, 

 or gi'owth areas. 



Before proceeding further with the description and inter]:)reta- 

 tion it may be well to emphasize the following cardinal facts: (1) 

 The embryonic heart-musculature is a syncytium composed of 

 anastomosing stellate and fusiform myoblasts with continuous 



