INTERCALATED DISCS OF THE HEART OF BEEF 289 



the intercalated discs, but also the telophraginata, and the iso- 

 tropic and anisotropic substances, stand forth with almost the 

 same sharpness and clearness as in sections. 



III. DESCRIPTIVE 



a. The ventricular myocardium 



There are no striking numerical or structural differences be- 

 tween the intercalated discs of the right and left ventricles. 

 Nor do appreciable differences occur between the atria and ven- 

 tricles, contrary to the opinion of Werner (23). As regards the 

 ventricular wall, the intercalated discs appear somewhat more 

 numerous in the papillary muscles and in the moderator band, 

 than in the more peripheral myocardium. Moreover, the discs 

 of the moderator band, and to some extent those also of the 

 papillary muscles and the columnae carneae, are less compli- 

 cated structures, that is, they are more generally of the simple 

 band form. The numerical difference may inhere largely in the 

 fact of less coarse and therefore relatively more abundant 

 trabeculae in the papillary musculature. The structural dif- 

 ferences are probably incidental to the generally different dis- 

 position of the branches at wider angles with respect to the 

 coarser trabeculae, thus producing more oblique stresses during 

 contraction, and to the spiral twistings of the muscle fibers dur- 

 ing development and growth, in the ventricular myocardium. 

 Neither the numerical nor the structural differences, however, 

 have fundamental significance. Structural differences are largely 

 the result of secondary modifications of originally very similar 

 and simple discs. We may quite securely begin the description 

 of the structural variations of the discs wdth the general propo- 

 sition that they are in all parts of the heart-musculature essen- 

 tially of the same nature, variety, and abundance. Such varia- 

 tions as occur in normal and pathologic hearts are incidental 

 respectively to normal and modified functional activity. 



The simplest type of disc in the adult heart is similar to those 

 which first appear in the fetal heart, and resembles a peripheral 



