MOliPHOLOCY OF IIKillER TYPES 



113 



each cell. Such muscles are capable of only relatively slow contrac- 

 tions, such as the movement of some of the visceral organs, for example 





Fig. 75. 



Fig. 76. 



Fig. 75. — A sarcostyle, diagrammatically represented, db, dark band; lb, light band 

 with a thin band of dark material dividing it into two portions. 



Fig. 76. — General appearance of striated muscle. A, part of a muscle fiber of a frog; 

 B, part of a fiber teased out to show fibrillse; db, dark bands; lb, light bands; /, fibrilla; 

 71, nucleus; s, sarcolemma. (From Parker and Haswell's Textbook of Zoology, after Huxley.) 



the walls of the Intestinal tract whose rhythmical contraction, or peri- 

 stalsis, is due to siaooth. muscle. Striated mus- .••.•;.'.";•. 

 cles are composed largely of longitudinal fi- 

 brillse or sarcostyles (Fig. 75) which are marked 

 by alternate hght and dark bands giving the 

 muscle cell as a whole a cross-striated appear- 

 ance (Fig. 76). The striated muscle cell is 

 not a simple cell, but a syncytium, that is, an 

 undivided mass of protoplasm containing many 

 nuclei, produced by failure of the cytoplasm to 

 divide after nuclear division. The structure 

 of striated muscle in cross-section is shown in 

 Fig. 77. Examples of muscle of this type are 



— C/ 



Cross section of 



found in wing and leg muscles of insects and ^, ^*^fj" .°^ striated 



Fig. 77. 



muscle. 

 The fibrillse are arranged in 



in limb or trunk muscles of vertebrates. Stria- bundles which are separated 



ted muscle, UnUke smooth muscle, is capable from each other by sarcoplasm. 



'_ _ ; t- ^i^ connective tissue: inn, nu- 



of very rapid contraction. cleus of muscle; net, nucleus 



Muscle tissue is classified on a physio- f connective tissue; si, sarco- 



* -jT 1 lemma. 



logical basis as voluntary or involuntary. Vol- 

 untary muscle is directly under the control of the will while involuntary 



8 



