580 Comparative Animal Physiology 



TABLE 70. KEY TO HISTOLOGICAL TYPES OF MUSCLE 



Type 



Striations 



Fibers 



Sarcoplasm 



Fibrils 



Example 



Striated 



Transverse, 

 distinct 



Long, non- 

 anastomosing 



Very litde, 



fibrils 

 nearly fill 

 fiber 



Distinct, striation 

 very sharp, 

 fibers some- • 

 times branched 



Arthropod 

 skeletal 

 muscle 



Abundant, stri- 

 ations less dense, 

 nuclei peripheral 



Vertebrate 

 white 

 muscle 



High sarco- 

 plasm-fibril 

 ratio, loosely 

 packed fibers 



Adult muscle: 

 nuclei usually 

 peripheral, 

 sometimes cen- 

 tral 



Vertebrate 

 red 

 muscle 



Embryonic 

 muscle: fibrillae 

 peripheral; 

 nuclei often 

 central, stria- 

 tions in process 

 of differentia- 

 tion 



Vertebrate 

 embryonic 

 muscle 



Branched, 



anastomosing 



Intercalated 

 discs prominent 



Vertebrate 

 cardiac 

 muscle 



No intercalated 

 discs 



Arthropod 

 cardiac 

 muscle 



Faint, may 

 be transverse, 

 diagonal, zig- 

 zag, spiral or 



Molluscan, 



annelid, 



ascidian 



striated 



fibers 



Non-striated 



Long, rarely 

 branches or 

 bridges 



Fibrils 

 readily 

 seen 



Phascolosoma 



retractors, 



cephalopod 



chromatophore 



muscles 



Fibrils 

 not readily 

 seen 



Echinoderm 

 (Thyone) re- 

 tractors, 

 molluscan 

 adductors 

 (smooth part) 



Less than 

 0.5 mm. long 



Fibrils usually 

 seen in cross 

 section, some 

 interfibrillar 

 bridges 



Vertebrate 

 smooth 

 muscle 



