MUSCULAR FIBEES OF THE HEART. 587 



around the fibres on the outside of the sarcolemma. 

 No vessels penetrate the sarcolemma to enter the interior 

 of the fibre. 



Nerves also are supplied freely to muscles ; the volun- 

 tary muscles receiving chiefly nerves from the cerebro- 

 spinal system, and the unstriped muscles from the sym- 

 pathetic or ganglionic system. 



Properties of Muscular Tissue. 



The property of muscular tissue, by which its peculiar 

 functions are exercised, is its contractility, which, in 

 the contraction or shortening of muscle, is excited by all 

 kinds of stimuli, applied either directly to the muscles, or 

 indirectly to them through the medium of their motor 

 nerves. This property, although commonly brought into 

 action through the nervous system, is inherent in the mus- 

 cular tissue. For 1st, it may be manifested in a muscle 

 which is isolated from the influence of the nervous system 

 by division of the nerves supplying it, so long as the natural 

 tissue of the muscle is duly nourished; and 2ndly, it is 

 manifest in a portion of muscular fibre, in which, under 

 the microscope, no nerve -fibre can be traced. 



If the removal of nervous influence be long continued, 

 as by division of the nerve supplying a muscle, or in cases 

 of paralysis of long-standing, the irritability, i.e., the 

 power of both perceiving and responding to a stimulus, 

 may be lost; but probably this is chiefly due to the 

 impaired nutrition of the muscular tissue, which ensues 

 through its inaction (J. Reid). The irritability of muscles 

 is also of course soon lost, unless a supply of arterial blood 

 to them is kept up. Thus, after ligature of the main 

 arterial trunk of a limb, the power of moving the muscles 

 is partially or wholly lost, until the collateral circulation is 

 established ; and when, in animals, the abdominal aorta is 

 tied, the hind legs are rendered almost powerless (Segalas). 

 So, also, it is to the imperfect supply of arterial blood to 



