STRUCTURE 



59 



where hairs occur, in the form of flattened roundish bundles which lie along- 

 side the hair follicles and sebaceous glands. 



Structure. Unstriated muscle fibers are elongated, spindle-shaped 



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.) 



mononucleated cells, 7 to S/j. in diameter by 40 to 2Oo/z in length, figures 

 68 and 69. The protoplasm of each cell, the contractile substance, is 

 marked by longitudinal striations representing fibrils which have been 

 described as contractile. The nucleus is an oblong mass placed near the 



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 t Sarcolemma; B, Krause's membrane. The sarcolemma shows regular 

 bulgings. Above and below Krause's membrane are seen the transparent "lateral discs." 

 The chief mass of a muscular compartment is occupied by the contractile disc composed 

 of sarcous elements. The substance of 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 network. X 300. (Klein and 

 Noble Smith.) 



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 



