HEART MUSCLE 



(51 



In transverse section, figure 70, the area of the muscle substance is mapped 

 out into small polygonal areas by a network of clear lines called Cohnheim's 

 areas. The lines represent the substance between the sarcostyles. This 

 substance probably represents the less differentiated contractile substance, 

 called sarco plasm. In figure 81 the interfibrillar sarcoplasm is indicated 

 by the longitudinal and transverse lines. 



Heart Muscle. The muscle substance of the heart is composed 

 of mononucleated masses of protoplasm, cardiac muscle cells, in which the 

 substance of the cell presents the transversely striated appearance char- 

 acteristic of the voluntary muscle just 

 described. But the heart muscle is phys- 

 iologically much more like an involuntary 

 muscle. The cells are rather small, two 



i .jfc.. .11 



to four times as long as thick, and the nu- 

 A y | cleus is usually situated near the middle of 



FIG. 77. 



FIG. 78. 



FIG. 77- A Section of Cardiac Muscle, Diagrammatic. (From E. A. Schafer, after Heiden- 

 hain.) 



FIG. 78. Intercellular Continuity of Muscle Fibrils in Cardiac Muscle. (From E. A. Schafer 

 after Przewosky.) 



the cell, figure 79. There is no sarcolemma; on the other hand, the cells 

 present branched and irregular outlines, but adjacent cells interlock in 

 close-fitting contact. 



Certain observers have described fibrils as extending across the so-called 

 cell boundary and noted that not all such boundaries enclose nuclei. These 

 observations suggest that cardiac muscle belongs to the group of tissues 

 possessing a syncytium. However, the section of cardiac tissue may very 

 possibly cut many cells without enclosing a nucleus. The continuity of 



