408 Walter J. Meek. 



appears at a given level each one probably belongs to a separate 

 so-called fiber. The territory of each fiber is, however, impossible 

 to determine, a fact that is due to the irregular arrangement of the 

 fibrils. Fig. G illustrates this point. Here two nuclei appear and 

 one would judge that at least two fibers composed the trabecula, but 

 it would be impossible to divide the fibrillar area into two very 

 definite regions. This fact is due to the free branching and anas- 

 tomosing of the fibers within the primary trabeculse. Since these 

 secondary strands have no well defined boundaries, yet branch and 

 fuse with each other, the heart muscle must be considered a syncytium. 

 In a syncytic structure one can scarcely speak of definite cells or 

 fibers and this is plainly borne out by the confused fibrillar areas in 

 the cross sections of the trabecule. The contractile elements form 

 strands which branch and fuse. These strands may be called fibers 

 or cells for convenience, but they must not be confused in structure 

 with such fibers as we have in skeletal muscle. 



In longi sections, cross and longi striation is well brought out by 

 the iron hsematoxylin method. As in the heart muscle of all other 

 forms it is evident that each contractile fibril is continuous through- 

 out the entire musculature, ending only where the muscle fiber itself 

 takes its origin. The clear areas of the cross sections now appear 

 as longitudinal clefts mostly filled with protoplasm. In these lie the 

 muscle nuclei. Fig. 8 shows a trabecula illustrating these points. 

 These muscle nuclei are long and narrow in diameter, with edges 

 which curve out toward the membrane of Krause. There is a scant 

 chromatin network and at least one nucleolus is usually visible. 

 The fibrils are grouped into strands, which illustrates the inner syn- 

 cytic structure already discussed. Outside of these strands is again 

 seen the cylinder of protoplasm and outside of this the fine linear 

 boundary (c and f in Fig. 8). The peripheral nuclei are now seen 

 to be oval in shape. They equal the muscle nuclei in diameter, but 

 otherwise do not resemble them closely. The boundary membrane 

 appearing as a fine line (/ in Fig. 8) is attached to the Z line of 

 the muscle fiber, the membrane of Krause, and for this reason it 

 appears in a series of festoons rather than a straight line. It has 

 proved quite a task to decide what relation this outer protoplasmic 



