Striietnro of Siiiooth ]\riisclo. 509 



syncytium. AVlierc some of the cells ave iii(l<'|)en(lciit, others con- 

 nected, the term partial syncytium is used. 



a. Smooth muscle with complete syncytial structure. 



When viewed in longitudinal section it is easily demonstrated that 

 in some adult smooth muscle there is a persistence of the embryonal 

 syncytium. The smooth muscle fibers are united by larger or smaller 

 protoplasmic strands so that independent cells are not present. This 

 arrangement is found in the intestine and bladder of IsTecturus, in the 

 bladder of the frog, in the stomach and intestine of the chicken, and 

 in portions of the digestive tract of dog, cat, pig and man. Muscle 

 of type 1 is not found in all of the muscle in the regions cited. Fibers 

 showing only end to end union often occur in portions while neighbor- 

 ing portions may show l)oth end and side anastomoses. 



Text Fig. 1. 

 Syncytial smooth muscle from the intestine of adult pig. X ^^'O- 



The idea that smooth muscle is a syncytium is not new. However, 

 most authors who have described it have found the cells united only 

 by very delicate protoplasmic strands, the sorcalled intercellular 

 bridges. Among these investigators may be mentioned Leydig, 1849 ; 

 Wagner, 1869; Flemming, 1878; Kultschitzky, 1888; B-arfurth, 

 1891; Heidenhain, 1893; Werner, 1894, and Bohemann, 1895. 

 The intercellular bridges were considered by most of these writers as 

 of secondary origin and not as the result of the persistence of an 

 embryonic syncytium. The improved connective tissue stains of recent 

 years, such as Mallory's anilin-blue mixture, Van Gieson's mixture, 

 and Mallory's phosphotungstic mixture, have shown that these fine 

 anastomoses between the muscle cells are chiefly connective tissue 

 strandsi. Figs. 20, 23, 27 and 34, and not true protoplasmic bridges. 



