SMOOTH OR NON-STRIATED MUSCLE 



SMOOTH OR NON-STRIATED MUSCLE. 



57 



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

 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 



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. 



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

 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 



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

 toplasmic 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; f, Fine myofibril; g, connective-tissue cell with 

 connective-tissue fibrils surrounding it; h, elastic fiber. (New figure by Caroline McGill.) 



where hairs occur, in the form of flattened roundish bundles which lie 

 alongside the hair-follicles and sebaceous glands. 



Structure. Unstriated muscle fibers are elongated, spindle-shaped, 

 mononucleated cells, 7 to 8 p, in diameter by 40 to 200 //, in length, figures 

 68 and 69. The protoplasm of each cell, the contractile substance, is 

 marked by longitudinal striations representing fibrils which have been 

 described as contractile. The nucleus is an oblong mass placed near the 



