442 MOVEMENTS. 



advanced to account for the movement of cilia. There is no 

 muscular structure, no connection with the nervous system, 

 and there seems to be no possibility of explaining the move- 

 ment except by a bare statement of the fact that the cilia 

 have the property of moving in a certain way so long as they 

 are under normal conditions. As regards the physiological 

 uses of these movements, it is sufficient to refer to the physi- 

 ology of the parts in which cilia are found, where the pecu- 

 liarities of their action are considered more in detail. In 

 the lungs and the air-passages generally, and the genital 

 passages of the female, the currents are of considerable im- 

 portance ; but it is difficult to imagine the use of these move- 

 ments in certain other situations, as the ventricles of the 

 brain. 



Movements due to Elasticity. There are certain impor- 

 tant movements in the body that are due simply to the action 

 of elastic ligaments or membranes. These are entirely distinct 

 from muscular movements, and are not even to be classed 

 with the movements produced by the resiliency of muscular 

 tissue, in which that curious property, called muscular toni- 

 city, is more or less involved. Movements of this kind are 

 never excited by nervous, galvanic, or other stimulus, but 

 consist simply in the return of movable parts to a certain 

 position after they have been displaced by muscular action, 

 and the reaction of tubes after forcible distention, as in the 

 walls of the large arteries. 



Elastic Tissue. Most writers of the present day adopt 

 the division of the elastic tissue, first made by Henle, 1 into 

 three varieties. This division relates to the size of the 

 fibres ; and all varieties are found to possess essentially the 

 same chemical composition and general properties, includ- 

 ing the elasticity for which they are so remarkable. On 

 account of the yellow color of this tissue, presenting, as it 

 does, a strong contrast to the white, glistening appearance 



1 HENLE, Traite & anatomic generale, Paris, 1843, tome i., p. 430. 



