SMOOTH MUSCLE 



Along the sides of the muscle fibers there are at first protoplasmic 

 processes which bind them together. Later these seem to be replaced 

 by white fibers, like those of ordinary connective tissue. They form a 

 network investing the muscle cells, as shown in Fig. 104. This inter- 

 muscular reticulum, produced directly from the muscle fibers, is unusually 

 well shown in the walls of the blood vessels in the umbilical cord. To 

 some extent, according to Miss McGill, it is produced from special mesen- 



FIG. 103. FROM A LONGITUDINAL SECTION OF 

 THE (ESOPHAGUS OF A 27-MM. PIG EMBRYO. 



X 700. (After McGill.) 

 b. m., Basement membrane; epi., epithelium; 



mes., mesenchyma; m. m., muscularis mucosse; 



n., nerve cells; s. c., circular smooth muscle 



cut across; s. 1., longitudinal smooth muscle 



cut lengthwise. 



FIG. 104. FIBROUS TISSUE IN 

 RELATION WITH SMOOTH 

 MUSCLE FIBERS, FROM THE 

 BLADDER OF A PIKE. (After 

 Prenant.) 



c., Connective tissue network; 

 n., p., f., nucleus, granular 

 protoplasm, and fibnllar pro- 

 toplasm of a muscle cell. 



chymal cells within the muscle layer, which develop into connective tissue 

 cells. In many layers of smooth muscle, however, connective tissue cells 

 are difficult to demonstrate. Finally it should be noted that elastic 

 fibers are found between the muscle cells. They vary greatly in number, 

 being especially abundant in the walls of arteries. 



From what has been said, it is evident that smooth muscle retains its 

 original syncytial nature, and that to some extent it resembles connective 

 tissue. It consists of elongated contractile cells which are joined together, 

 especially toward their extremities, by myoglia fibrils, and which are 

 bound together laterally by a white fibrous network containing inter- 



