MUSCULAR MOTION. 457 



one of the edges, either by a fine continuous dark streak, or 

 by short isolated dark lines, or by dark points arranged in a 

 row, or scattered. These fibre-cells, by their union, form fibres 

 and bundles of fibres (Fig. 156). The fibres have no distinct 

 sheath. 



The fibres of involuntary muscle, such as are here described, 

 form the proper muscular coats of the digestive canal from 

 the middle of the O3sophagus to the internal sphincter ani, of 

 the ureters and urinary bladder, the trachea and bronchi, the 

 ducts of glands, the gall-bladder, the vesiculaB seminales, the 

 pregnant uterus, of bloodvessels and lymphatics, the iris, and 

 some other parts. 



This form of tissue also enters largely into the composition 

 of the tunica dartos, and is the principal cause of the wrin- 

 kling and contraction of the scrotum on exposure to cold. The 

 fibres of the cremaster assist in some measure in producing 

 this effect, but they are chiefly concerned in drawing up the 



FIG. 157. 



Perpendicular section through the scalp, with two hair-sacs; a, epidermis; 6, 

 cutis ; c, muscles of the hair-follicles (after Kolliker). 



testis and its coverings towards the inguinal opening. Un- 

 striped muscular tissue occurs largely also in the cutis (p. 334), 

 being especially abundant at the interspaces between the bases 

 of the papillae. Hence, when it contracts under the influence 

 of cold, fear, electricity, or any other stimulus, the papillae are 

 made unusually prominent, and give rise to the peculiar 

 roughness of the skin termed cutis anserina, or goose-skin. It 

 occurs also in the superficial portion of the cutis, in all parts 

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

 which lie alongside the hair-follicles and sebaceous glands. 

 They pass obliquely from without inwards, embrace the seba- 

 ceous glands, and are attached to the hair-follicles near their 

 base (Fig. 157). 



