MUSCLES. . 4 



that the contractile element of which it is composed 

 is a spindle-shaped, or fusiform, corpuscle of variable 



length, in the interior of which a nucleus, which 



. 

 approaches more nearly the circular shape than that 



of the true smooth or unstriped fibre, is recognisable, 

 (PL XV. fig. VII. 2, 3.) We find this fusiform cor- 

 puscle in the walls of the villi of the small intestine, 

 in the muscles of the hair-bulbs, and perhaps also in 

 other organs. It is as yet an unsettled question 

 whether the dartos is made up of this element, or of 

 the fully developed unstriped fibre. 



The distribution of the smooth, or unstriped mus- Distribution of 



smooth muscular 



cular tissue, limited at first to organs possessed of 

 obvious contractility, is daily increasing in extent. 

 Thus, its presence has been demonstrated in the villi 

 of the intestines, in the excretory ducts of most of the 

 glands, in the middle coat of arteries, veins, and lym- 

 phatics, in the genital organs of the female (uterus 

 and appendages, vagina, and corpora cavernosa of the 

 clitoris) ; in the genital organs of the male (corpora 

 cavernosa penis, prepuce, prostate, seminal vesicles, 

 &c ) ; in the vascular tunic of the eye ; and, finally, 

 throughout the whole extent of the skin, where it is 

 very unequally distributed. It is found in connexion 

 with the hair-bulbs and sebaceous follicles ; and by 

 its presence, the phenomenon of horripilation, or 

 goose-flesh, is explained. Some portions of the ex- 

 ternal integument are unusually rich in unstriped 

 muscular fibres ; for example, the prepuce, and the 

 skin of the nipple, and in some instances, of the whole 

 female breast. The elongation and rigidity of the 

 nipple are due entirely to their contraction, and not, 



