6 4 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



Development. The striated muscle of the voluntary variety is usually 

 developed from the mesoderm. The embryonic cells increase enormously 

 in size, the nuclei multiply by fission and distribute themselves beneath the 



FIG. 81. 



FIG. 82. 



FIG. 81. Two Striped Muscle Fibers of the Hyoglossus of Frog, a, Nerve end-plate; 

 !) , nerve fibers leaving the end-plate; c, nerve-fibers terminating after dividing into branches; 

 d, a nucleus in which two nerve fibers anastomose. X 600. (Arndt.) 



FIG. 82. Developing Striated Muscular Fibers, Showing Different Stages of Develop- 

 ment and Different Positions of the Unstriated Protoplasm. A. Elongated cell with 

 two nuclei; the longitudinal striation is beginning to show on the right side. From a fetal 

 sheep. (Wilson Fox.) B. -Developing muscular fiber, showing * both longitudinal 

 and transverse striations at the periphery, and a central unstriated cylinder of protoplasm 

 containing several nuclei. From a human fetus near the third month. (Ranvier.) n, 

 Nucleus (there is usually a mass of glycogen near each nucleus); p, central unstriated 

 protoplasm; s, peripheral striated substance. C. Developing muscular fiber, showing a 

 lateral position of the unstriated protoplasm. From a three months' human fetus. 

 (Ranvier.) n, Nucleus; g, unstriated protoplasm at one side of the fiber; s, striated sarcous 

 substance with longitudinal and transverse striations. 



sarcolemma. There is a differentiation of the cell protoplasm which takes 

 place by the formation of sarcostyles. This begins nearest the surface of 

 the cells and proceeds toward the center of the mass. 



