Slnu'turc of Smooth ;M\isc1o. 515 



The fine mjofibrillse in some muscle become very numerous in the 

 later stages, and in the adult the muscle fiber may be well filled with 

 them. They are often the only fibrillse present. This is usually the 

 case in the intestinal muscle of Nocturus, Figs. 6, 23, 24 and of the 

 chicken, Figs. 2, 11. In the muscle of the digestive and urino- 

 genital tracts of mammals at times there are present none but fine 

 myofibrillse. Fig. 15. In cross section the fine myofibrillse appear as 

 fine dots. Figs. 16, 26. 



In the adult smooth muscle coarse myofibrillge may or may not be 

 present. When present they are occasionally the only myofibrillse 

 found, as in portions of the muscularis mucosae of the small intestine 

 of the pig, Fig. 17, and in the carotid of the ox. Fig. 4 a. Usually, 

 however, they are associated with fine myofibrilla?. In this relation 

 they were foimd in large numbers in the carotid of the ox, Fig. 5, 

 and in the muscularis niucosa3 of the oesophagus of the pig. As 

 occasional structures they occur throughout the muscularis of the 

 digestive tract of dog, cat, pig, and man. !N^o coarse myofibrillse 

 were found in the smooth muscle of Kecturus notwithstanding the 

 fact that in Salamander, a closely allied form, Heidenhain, 1900, 

 found them in large numbers. 



When coarse myofibrillse alone are present, they may be arranged 

 as a peripheral layer, Fig. 17, or they may be scattered throughout 

 the entire diameter of the fiber, Fig. 4 a. When associated with fine 

 myofibrillse, they may likewise occupy a peripheral position only. 

 Fig. 4 b. They then correspond to the "Grenzfibrillen" described 

 by Heidenhain, 1900. More often the coarse myofibrillse are 

 scattered throughout the muscle cell. They then approach in arrange- 

 ment more nearly the coarse myofibrillse described by Benda, 1902. 



In uncontracted muscle the coarse myofibrillse of the adult are of 

 approximately even caliber throughout the entire length. They stain 

 very intensely in eosin or in iron-hsematoxylin. Iron-hsematoxylin 

 stains the coarse myofibrillse long after it has been extracted from the 

 fine myofibrillar so that usually in an iron-hsematoxylin-eosin prepara- 

 tion the coarse myofibrillse are stained black, the fine myofibrillse 

 red. In the muscle syncytium l)otli types of fibrillse run past the 

 limits of one cell, through the anastomoses into neighboring cells, 

 Figs. 13-15. 



