CHAP. VI.] THE MUSCLES. 55 



nucleoli. The substance of the fibre-cell is longitudinally stri- 

 ated, but does not exhibit transverse striation. The fibre-cells 

 lie side by side, or lap over one another at the ends, and are 

 joined together by a small amount of cement substance. 



This kind of muscular tissue is found arranged around the 

 blood-vessels and most of the hollow viscera. The fibres are 

 variously grouped in different parts of the body ; sometimes 

 crowded together in solid bundles, which 

 are arranged in layers and surrounded by 

 connective tissue, as in the intestines ; 

 sometimes arranged in narrow interlacing 

 bundles, as in the bladder; sometimes wound 

 in single or double layers around the blood- 

 vessels ; and again, running in various direc- 

 tions and associated with bands of connec- 

 tive tissue, they form large compact masses, 

 as in the uterus. 



Numerous nerves are supplied to non- 

 striated muscular tissue, and many blood- 

 vessels. 



The contraction of this kind of muscular 

 tissue is much slower and lasts longer than 

 the contraction of the striated variety. As 



i i ,1 T c ,1 11, FIG. 54. FIBRE-CELLS 



a general rule the muscles of the skeleton OF PLAIN MUSCULAR 

 are thrown into contraction only by nervous TISSUE. Highly magni- 

 impulses reaching them along their nerves ; 

 spontaneous contractions, as in a case of "cramps," being rare 

 and abnormal. The plain muscular tissue of the internal 

 organs, however, very often contracts independently of the 

 central nervous system, and under favorable circumstances will 

 continue to do so after the viscera have been removed from the 

 body. 



The great increase in the muscular tissue of the uterus during gestation 

 takes place both by elongation and thickening of the pre-existing fibre-cells, 

 and also, it is thought, by the development of new fibre-cells from .small 

 granular cells lying in the tissue. In the shrinking of the uterus after par- 

 turition the fibre-cells diminish to their previous size ; many of them become 

 filled with fat granules, and eventually many are, doubtless, removed by 

 absorption. 



Development of striated muscular tissue. When the muscular fibres 

 are about to be formed, the cells set apart for this purpose elongate, and their 



