538 PHYSIOLOGY. 



tributed upon the outer surface of the sarcolemma, where there is 

 formed a plexus. This plexus winds round the muscle-fiber. 



Cardiac Muscle. Some mention has previously been made con- 

 cerning cardiac muscle, so that at this point only its most striking 

 peculiarities will be mentioned, and that cursorily, (a) It is a 

 striped muscle. However, its striations are not nearly so distinctly 

 marked as are those of voluntary muscle. Occasionally it is noticed 

 to be marked longitudinally, (b) Cardiac muscle-fibers possess no 

 sarcolemma. (c) Its fibers branch and anastomose, (d) The nucleus 

 is placed in the center of each cell. One author says that cardiac 

 muscle stands, physiologically, midway between striped and unstriped 

 muscle. When stimulated, its contractions occur slowly, but last for 

 a considerable length of time. 



Nonstriped Muscle. These muscles are made up of a number of 

 contractile fiber-cells, of an elongated, fusiform shape, usually 

 pointed at the end. These fiber-cells may be readily demonstrated 

 by placing the tissue in a strong alkaline solution or in a solution 

 of strong nitric acid. 



Upon transverse section they are generally prismatic, but some- 

 times are more flattened. Their muscle-substance is doubly refract- 

 ing. Each cell has a nucleus which is either elongated or oval. It 

 may contain one or more nucleoli. The nucleus is brought into 

 view by means of dilute acetic acid or staining reagents. 



The involuntary fiber-cells have a delicate sheath, which, like 

 the sarcolemma of voluntary muscle-fiber, is very apt to become 

 wrinkled when the fiber is contracted. By reason of this an indis- 

 tinctly striated appearance may be produced. 



While fiber-cells do occur singly, yet it is more common for them 

 to be found in groups. Thus, muscular sheets, or bundles, are pro- 

 duced which may cross one another and interlace, being held in posi- 

 tion by enveloping connective tissue. The individual cells are united 

 by the presence of a very delicate cement. 



The average length of the fiber-cells rajiges from V 100 to Vaoo 

 of an inch ; those forming the middle coat of the arteries are shorter, 

 those in the intestinal tract and pregnant uterus are considerably 

 longer. 



WHERE FOUND. The unstriped muscular tissue is more gen- 

 erally distributed within the body than one would suppose. It is 

 found in the lower part of the oesophagus, in the stomach, small and 

 large intestines; in arteries, veins, and lymphatics; in the ureters, 

 bladder, and urethra; in the internal female generative organs, etc. 





