496 Caroline McGill. 



protoplasmic strands, with tho muscle protoplasm. Often in a single 

 protoplasmic mass connective tissue fibers and myofibrillse differen- 

 tiate side by side. In later development most of the connective tissue 

 fibrils are crowded out of the muscle bundles by the rapidly developing 

 myofibrillse, though some may, even in the adult, retain their primitive 

 relation. As the myofibrillse fonn, they tend to run in longitudinal 

 bundles, but always show marked side anastomoses with neighbor- 

 ing bundles. Throughout development, and in many instances 

 in the adult, this syncytium persists. In the adult the syncytial 

 arrangement was demonstrated in the muscle of the digestive tract 

 of Necturus, dog, cat, and pig. 



2. On the structure of contracted smooth muscle. 



The literature on the structure of contracted smooth muscle is 

 reviewed in detail by Heiderich, 1902, consequently only the more 

 important references dealing directly with the subject will be given 

 in this paper. 



The earlier writers on the structure of contracted smooth muscle 

 held that the tissue shortens by a zigzag folding of the fibers. Among 

 the investigators who supported this view may be mentioned Prevost 

 and Dumas, 1823, Kemak, 1813, Leydig, 1849, Mazonne, 1851, 

 Meissner, 1858, Schwalbe, 1868, Arnold, 1871, Eouget, 1881, and 

 Marshall, 1887. Shultz, 1895, considered that all zigzag folding and 

 wrinkling of smooth muscle fibers indicate contraction in the absence 

 of tension. 



In opposition to the zigzag theory of contraction, Kolliker, 1849, 

 working on the smooth muscle of the ureter, prostate and small intes- 

 tine of several forms, described knotlike thickenings in the contracted 

 fibers which he considered contraction areas. 



Heidenhain, 1861, found two types of contraction in smooth 

 muscle: (1) A peristaltic, where the fibers show knotlike contraction 

 areas with uneontracted areas between; (2) a general or total where 

 there is a shortening and thickening of the entire fiber. The latter 

 type only he held as normal. 



Margo, 1862, found, as did Meissner: a cross-striation of the con- 

 tracted smooth muscle fiber, not due, however, to wrinkles, but to 

 rows of small granules analogous to the sarcous elements of striated 

 muscle. 



