88 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



also some pigment. The latter is more prominent in 

 old hearts, to which it imparts a brown color. 



At present the exact structure of the heart muscle 

 is a disputed question. In sections, many breaks 

 or artifacts resemble the cement lines separating 

 adjacent cells. The longitudinal fibrils are said to 

 penetrate the cement and thus establish a con- 

 tinuity of protoplasm between adjacent cells. The 

 presence or absence of a cell wall, analogous to the 

 sarcolemma of voluntary muscle, is also disputed. 



3. Voluntary Muscle. A voluntary muscle fiber 

 is a multinucleated, greatly elongated cell, which 

 may attain a length of 12 cm. (5 inches). These 

 fibers are arranged parallel to each other and grouped 

 into bundles, called fasciculi. Each fasciculus, is 



Sarcoslyles. 



Fig- 55- Voluntary muscle fiber. The sarcoplasm has broken, show- 

 ing the smooth sarcolemma. 



surrounded by connective-tissue cells and fibers in 

 which many blood-vessels ramify. A finer fabric of 

 connective tissue penetrates the fasciculus and gives 

 support to the individual fibers. The connective 

 tissue that enters a fasciculus is called the endo- 

 mysium, and that which surrounds a fasciculus is 

 called the perimysium. Fasciculi are grouped into 

 coarser bundles and these collectively make up a 

 muscle. The muscle is in turn enveloped in a firm 

 connective- tissue layer called the epimysium. In 

 gross anatomy the latter constitutes the deep fascia 



