114 



General Biology 



undivided cytoplasm ( •). There is a thin but well 



defined cell wall, called the sarcolemma ( ), best 



seen where the contents of the fiber are crushed or broken apart. 



Each fiber of voluntary muscle is regarded as a single cell with 

 numerous nuclei scattered throughout its cytoplasm. In the early stages 

 of development there is but one nucleus in each cell in the voluntary 

 muscle, but as the fiber grows and the nucleus rapidly divides, while the 



C 



c. 



Fig. 41. 



A. Smooth muscle fibers from the bladder of a Frog. 



B. Heart-muscle syncitium. 



C. Striated muscle fibers from the muscle of a cat. Q, cross discs separated 

 from each other by interposed discs II, 12. zz shows the stripe in which granules 

 are visible, h, is shown as a center-disc, situated within the cross-disc. (From 

 Krause-Schmahl "Histology," by permission of The Rebman Co.) 



cytoplasm does not, there are naturally a number of nuclei within a 

 single cell wall. 



There is here both a longitudinal and a cross striation consisting of 

 alternate light and dark bands. Sarcostyles ( ), or 



fibrillae, which extend the entire length of the cell, are the cause of the 

 longitudinal striations. These fibrillae, as in the unstriated muscle 

 fibers, are the contractile elements. They are kept apart by a semi- 

 fluid substance, called the sarcoplasm. The fibrillae themselves are 

 arranged in bundles or muscle columns separated from each other by a 



