THE MUSCULAR SYSTEM. 



395 



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, whirh 

 lie alongside the hair-follicles and sebaceous glands. They pass obliquely 



Fia. 272. A, unstriped muscle cells from the mesentery of a newt. The sheath exhibits trans- 

 verse markings. X 180. B, from a similar preparation, showing that each muscle cell consists of a 

 central bundle of fibrils, F (contractile part), connected with the intra-nuclear network, N, and a 

 sheath with annular thickenings, St. The cells show varicosities due to local contraction and on 

 these the annular thickenings are most marked. X 450. (Klein and Noble Smith.) 



from without inwards, embrace the sebaceous glands, and are attached to 

 the hair-follicles near their base (Fig. 271). 



Structure. TJnstriated muscles are made up of elongated, spindle- 



FIG. 273. Plexus of bundles of unstriped muscle cells from the pulmonary pleura of the guinea, 

 pig. X 180. (Klein and Noble Smith.) A, branching fiores; B, their long central nuclei. 



shaped, nucleated cells (Fig. 272), which in their perfect form are flat, 

 from about T ^ir * srVir f an i ncn broad, and -g J to -%%-$ of an inch in 

 length very clear, granular, and brittle, so that when they break they 

 often have abruptly rounded or square extremities. Each cell of these 

 consists of a fine sheath, probably elastic; of a central bundle of fibrils, 

 representing the contractile substance; and of an oblong nucleus, which 



