Structure of Smooth Muscle. 513 



o. Smooth muscle with apparently isolated fibers. 



13j far the majority of writers on the structure of smooth muscle 

 have described it as everj-where made up of entirely free and inde- 

 pendent spindle-shaped elements, the so-called muscle fibers, muscle 

 cells, or muscle spindles of Kolliker, 1849. Such an element is 

 diagrammatically represented in text Figs. 3, 4, Recent advocates 

 of this idea are Heidenhain, 1900 ; lleiderich, 1902 ; Forster, 

 1904; Schlater, 1905, and Soli, 1906. 



In the material studied in this investigation it was found exceed- 

 ingly difficult to demonstrate isolated smooth muscle fibers. In the 

 walls of the carotid of the ox some of the fibers appear to be free. 

 Fig. 33. Here the fibers are long, slender structures, thicker in the 

 vicinity of the nucleus than elsewhere. Because of their length and 

 the curved course they take in surrounding the lumen (most of them 

 are circular fibers) it is possible in only a few places to get them cut 

 in exactly longitudinal section. It should be remembered that 

 spindles appearing independent in such sections may appear so 

 because the section is cut slightly obliquely. In these sections anas- 

 tomosis of fibers end to end would not show even if present. Further- 

 more, a tangential section of a spindle-shaped fiber may look like an 

 isolated fiber. Consequently it is not surprising that end to end 

 union is hard to demonstrate in arterial muscle fibers. In many 

 instances end anastomoses do occur, so even here there is at least a 

 partial syncytium. It is j)robable, too, that the syncytium is much 

 more nearly complete than sections would lead one to conclude. The 

 development of arterial muscle was not studied in detail, but in both 

 chick and pig the tissue arises as a complete syncytium. In all other 

 muscle studied the syncytial structure in the adult is more apparent 

 than in arterial muscle. 



Most of the work of earlier investigators on the general form of the 

 smooth muscle ccdl was done on macerated material. In maceration 

 the reagent usually destroys at least the peripheral myofibrillse, so 

 that fine anastomoses even if ]iresent are destroyed, leaving only the 

 central spindle-shaped portion of the cell intact. In this way are 

 undoubtedly obtainc*! many of the spindle-shaped cells figured in the 

 text-books. 



