58 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



III. MUSCULAR TISSUE. 



There are two chief kinds of muscular tissue, differing both in minute 

 structure as well as in mode of action, viz., (i) the smooth or non- striated, and 

 (2) the striated. 



SMOOTH OR NON-STRIATED MUSCLE. 



Non-striated muscle forms the proper muscular coats of the digestive 

 canal from the middle of the esophagus to the internal sphincter ani; of 

 the uterus and urinary bladder; of the trachea and bronchi; of the ducts 



FIG. 68. Isolated Smooth Muscle Cells from Human Small Intestine. X 400. Rod- 

 shaped nucleus surrounded by area of finely granular protoplasm; longitudinal striations 

 of cytoplasm. 



of glands; of the gall-bladder; of the vesiculae seminales; of the uterus and 

 Fallopian tubes; of the blood vessels and lymphatics; and of the iris and 

 some other parts of the eye. This form of tissue also enters largely into the 

 composition of the tunica dartos of the scrotum. Unstriped muscular tissue 



FIG. 69. Smooth Muscle from Intestine of Pig, Showing Syncytial Structure, a, 

 Protoplasmic process connecting two muscle fibers; b, end-to-end union of two muscle 

 fibers, showing the continuity of protoplasm and myofibrils; c, nucleus of muscle fiber; 

 d, granular protoplasm at the end of muscle nucleus; e, coarse myofibril;/, fine myofibril; 

 g, connective-tissue cell with connective-tissue fibrils surrounding it; h, elastic fiber. (New 

 figure by Caroline McGill.) 



occurs largely also in the true skin generally, being especially abundant in the 

 interspaces between the bases of the papillae, and, when it contracts, the 

 papillae are made unusually prominent, giving rise to the peculiar roughness 

 of the skin termed cutis anserina, or goose flesh. It also occurs in all parts 



