DEVELOPMENT 63 



which takes place by the formation of sarcostyles. This begins nearest the 

 surface of the cells and proceeds toward the center of the mass. 



The sarcolemma is apparently produced from embryonic connective 

 tissue. 



The cardiac muscle cells are at first spindle-shaped embryonic cells 

 which elongate more and more. In further differentiation their protoplasm 



FIG. 8 1. 



FIG. 82. 



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

 Different Positions of the Unstriated Protoplasm. A. Elongated cell with two nuclei; the longi- 

 tudinal 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 protoplas-n; s, peripheral striated substance. C. Developing mus- 

 cular fiber, showing a lateral position of the unstriated protoplasm. From a three-months' human 

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

 sarcous substance with longitudinal and transverse striations. 



exhibits faint striations which pervade the cell as it grows in the great increase 

 in size. The rhythmic contractions begin long before the striations appear. 



