58 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



center of the cell. It is covered by a nuclear membrane which encloses a 

 network of anastomosing fibrils. 



Development. In the pig the smooth muscle of the alimentary 

 canal originates in the syncytium of the mesodermal cells which surround 

 the entoderm. The cells soon begin to grow into the adult spindle-shape 

 form and the fibrils make their appearance. Even in the adult muscle the 

 syncytial connections are retained according to Miss McGill. 



Striated Muscle. 



Striated or striped muscle constitutes the whole of the muscular apparatus 

 of the skeleton, of the walls of the abdomen, the limbs, etc. the whole 



FIG. 70. Transverse Section through Muscular Fibers of Human Tongue. The deeply stained 

 nuclei are situated at the inside of the sarcolemma. Each muscle fiber shows Cohnheim s fields, 

 that is, the sarcous elements in transverse section separated by clear (apparently linear) interstitial 

 substance. X 450. (Klein and Noble Smith.) 



FIG. 71. 



FIG. 72. 



FIG. 71. Muscle Fiber Torn Across; the sarcolemma still connects the two parts of the fiber. 

 (Todd and Bowman.) 



FIG. 72. Part of a Striped Muscle Fiber of a Water Beetle prepared with Absolute Alcohol. 

 A, Sarcolemma; B, Krause's membrane. The sarcolemma shows regular bulgings. Above and 

 below Krause's membrane are seen the transparent " lateral discs." The chief massof a muscular 

 compartment is occupied by the contractile disc composed of sarcous elements. The substance ot 

 the individual sarcous elements has collected more at the extremity than in the center; hence this 

 latter is more transparent. The optical effect is that the contractile disc appears to possess a 

 "median disc" (Disc of Hensen). Several nuclei, C and D, are shown, and in them a minute net- 

 work. X 300. (Klein and Noble Smith.) 



of those muscles which are under the control of the will and hence termed 

 voluntary; also the muscle of the heart. 



