Structure of Smooth Muscle. 495 



very favorable material, especially for experimental work. The 

 description of contraction in invertebrate smooth muscle along with a 

 review of the literature on the subject is reserved for a later paper. 

 This work was done in the Anatomical Laboratory of the Uni- 

 versity of Missouri under the direction of Prof. C. M. Jackson, to 

 whom I am indebted for many valuable suggestions. 



II. LiTERATUKE KeVIEW. 



1. On the structure of resting smooth muscle. 



For the literature on the general structure of smooth muscle, the 

 reader is referred to the excellent review given by M, Heidenhain, 

 1900. Since 1900 several papers have appeared. Henneberg, 1901, 

 Heiderich, 1902, Forster, 1904, Schlater, 1905, and Soli, 1906, 

 describe smooth muscle as though made up of entirely separate and 

 distinct cells. 



The following are the main references to the syncytial structure of 

 smooth muscle: Drasch, 1895, in the skin of the salamander, found 

 aiound the periphery of the large poison glands a complete layer of 

 smooth muscle fibers, united by wide protoplasmic anastomoses into a 

 syncytium. Schaper, 1902, in Urodela, found the smooth muscle 

 fibers in the mesentery anastomosing more or less and mentions the 

 probability that the tissue forms a syncytium. 



Eohde, 1905, in a comparative study of the smooth muscle in both 

 vertebrates and invertebrates, described protoplasmic connections not 

 only between smooth muscle cells, but also between muscle cells on 

 the one hand, and epithelium, ganglion cells and connective tissue 

 cells on the other. Rohde makes the assertion that these intercellular 

 bridges represent the remains of an embryonic syncytium. He gives, 

 however, neither figures nor descriptions of embryonic material to 

 support this view. 



McGill, (1), 1907, in the digestive tract of the pig found that 

 smooth muscle arises, in common with the interstitial connective tis- 

 sue, from the mesenchymal syncytium surrounding the endodermal 

 tube. Some of the mesenchyme cells in the area of muscle formation 

 do not elongate, but persist as the connective tissue cells, connected by 



