390 THE TISSUES. 



Functions of the Muscular Fibre- Cells. 



The tissues thus far described, have manifested physical proper- 

 ties only. But muscular fibre-cells are, like the striated muscular 

 fibres, endowed with a vital property, contractility, and the power of 

 contraction; or of spontaneously shortening themselves, when excited 

 by an appropriate stimulus. This latter is often brought to them 

 by a nerve ; but not always, nor so generally as is the case with 

 the striated fibres. Hence they are not so abundantly supplied 

 with the large (motor) nerve-fibres. In the alimentary canal, the 

 muscular coat is excited to contraction more especially by the con- 

 tents of the canal itself; and this is probably also true of the bron- 

 chial tubes, the blood- and lymph-vessels, the bladder and the 

 uterus. 



Hence, the motion is transmitted along a membraniform expan- 

 sion of smooth muscular fibre somewhat slowly. The fibres not 

 being bound up into parallel fasciculi to form muscles, but being 

 interwoven, and each contracting independently of the rest the 

 movement of the first excites the rest in contact with it, and thus 

 the action is propagated to a distance. This peculiarity has given 

 to the motions of the alimentary canal the name of vermicular or 

 peristaltic motion. The more or less rhythmical character of the 

 contractions of this kind of muscular fibre, is also probably due to 

 the anatomical peculiarity just mentioned. This is best seen in the 

 case of uterine contractions ; and also in cases of colic, and of cal- 

 culus in the bladder or in the ureters. 



The contractions of the smooth muscular fibres are not in the 

 least degree under the control of volition. Those who maintain 

 that parturition is in some instances voluntarily deferred (after it 

 actually commences at the end of the full term), and then again 

 voluntarily recommenced, are deceived by appearances which a 

 knowledge of the reflex function of the spinal cord at once explains 

 away. 



Where a required motion is to be of slight extent, internal, not 

 rapid, and not at all influenced by the will it is delegated to 

 the stnooth muscular fibre. When either or all of these require- 

 ments are to be reversed, the striated muscular fibre is employed 

 instead. It is therefore physiologically inferior to the latter. Histo- 

 logically, also, it may be regarded as a lower development, as will 

 appear. 



