216 TWO KINDS OF MUSCLE. 



described by Mr. Bowman in his well-known paper 

 (Phil. Trans. > 1841). The reader is also referred to 

 Mr. Bowman's article^ "Muscular Motion," in Todd's 

 Cyclopasdia of Anatomy and Physiology. 



260. Two kinds of muscle. The contractile ma- 

 terial of muscular tissue is arranged so as to form 

 fibres, plates, cords, or bands*, varying much in dimen- 

 sions and somewhat in minute structure. By examina- 

 tion with the aid of high magnifying powers we are 

 enabled to distinguish the different kinds of muscular 

 tissue, which may be arranged in two classes accord- 

 ing as the contractile tissue appears structureless, or 

 exhibits an appearance of longitudinal striation, distinct 

 transverse bars, striae, or stripes. The fibres of the 

 voluntary muscles (of those the movements of which 

 can be either excited or controlled by volition), as well 

 as the fibres of the heart, and some of those of the 

 oesophagus, are striped ; while all other muscles, in- 

 cluding those of the alimentary canal, the uterus, and 

 bladder, all of which are involuntary, are unstriped. 



261. Unstriped muscle. The unstriped muscular 

 tissue may be studied in many organs of vertebrata, 

 but the most favourable situation known to me, is 

 the bladder of the frog. In the thinnest parts of 

 this extremely delicate membrane the muscular fibres 

 or fibre- cells form a single layer, and are often sepa- 

 rated from one another, so that an individual ele- 

 mentary fibre may be followed from one end to the 

 other. Bundles of these long spin died- shaped ele- 

 mentary parts are arranged around all the vessels, 

 but in the intercapillary spaces are numerous separate 

 fibres which cross each other at various angles, and 

 are so arranged that when they contract, the area of 

 the membrane is reduced in every direction. In the 

 central part of each fibre or fibre-cell is the oval mass 

 of bioplasm (nucleus), at either end of which new con- 

 tractile material is produced as the fibre increases in 

 length. From these points the muscular band, 



