THE ESSENTIALS OF HISTOLOGY. 



Involuntary or plain muscular tissue is composed of long, some- 

 what flattened, fusiform cells (fig. 96), 

 which vary much in length, but are 

 usually not more than ^^ inch long. 

 Each cell has an oval or rod-shaped 

 nucleus, which shows the usual intra- 

 nuclear network and commonly one or 

 two nucleoli. The celL-substance is 

 longitudinally striated, but does not 

 exhibit cross-stria3 like those of volun- 

 tary muscle. There appears to be a 

 delicate sheath to each cell. There is 

 a little intercellular cementing sub- 

 stance uniting the cells together, which 

 can be stained by nitrate of silver, and 

 this intercellular substance is bridged 

 across by fine filaments passing from 

 cell to cell. The fibres are collected 

 into fasciculi. 



Plain muscular tissue is found chiefly 

 in the walls of hollow viscera ; thus it 

 forms the muscular coat of the whole 

 of the alimentary canal below the 

 oasophagus, and occurs abundantly in 

 the muscular coat of that tube also, 

 although it is here intermixed with 

 cross-striated muscle ; it is found also 

 in the mucous membrane of the alimen- 

 tary canal ; in the trachea and its rami- 

 fications ; in the urinary bladder and 

 ureters ; in the uterus, Fallopian tubes, 

 and ovary ; in the prostate, the spleen, 

 and muscle of Miiller in the orbit, and 

 in the ciliary muscle and iris. The 

 walls of gland-ducts also contain it, and 

 the middle coat of the arteries, veins, 

 and lymphatics is largely composed of 

 this tissue. It occurs also in the skin, 

 both in the secreting part of the sweat- 

 glands, and in small bundles attached to the hair-follicles; in the 

 scrotum it is found abundantly in the subcutaneous tissue (dartos), and 

 it also occurs in the areola of the nipple. 



FIG. 96. MUSCULAR FIBRE-CELLS 



FROM THE MUSCULAR COAT OF THE 

 SMALL INTESTINE, HIGHLY MAG- 

 NIFIED. 



A, a complete cell, showing the nucleus 

 with intra-nuclear network, and the 

 longitudinal fibrillation of the cell- 

 substance, with finely vacuolated 

 protoplasm between the fibrils ; B, a 

 cell broken in the process of isolation ; 

 a delicate enveloping membrane pro- 

 jects at the broken end a little beyond 

 the substance of the cell. 



