TISSUES, ORGANS, AND SYSTEMS. 89 



deferens, vesiculce seminales, the prostate, around Cowper's 

 glands, and in the corpora cavernosa penis. 



9. In the Vascular system smooth muscles exist in the 

 tunica media of all, especially of the smaller arteries ; also in 

 that of most veins, and of the lymphatics, with the exception of 

 the finest ; furthermore in the lymphatic glands (Hcyfelder) ; 

 and lastly in the tunica adventitia of many veins. The 

 elements, in vessels of middle dimensions, are everywhere fusi- 

 form fibre-cells ; in the large arteries, on the other hand, 

 shorter plates, which often resemble certain forms of pavement 

 epithelium; and in the smallest arteries they are more elongated, 

 or even round cells, forms which must be considered as less 

 developed. 



10. In the Eye, smooth muscles form the sphincter and 

 dilator papilla and the tensor choroidea. 



11. In the Skin, lastly, this tissue appears besides in the 

 dartos, in the form of minute muscles upon the hair sacs, in the 

 areola, and in the nipple, and in many of the sudoriparous and 

 sebaceous follicles. 



[The elements of the smooth muscles were formerly univer- 

 sally regarded as elongated bands containing many nuclei, which 

 were supposed to be developed by the coalescence of numerous 

 mutually applied cells. In 1847 I showed that this is not the 

 case ; that, on the other hand, the elements of these muscles 

 are only modified simple cells ; and at the same time I demon- 

 strated, that these contractile fibre-cells occur wherever con- 

 tractile connective tissue had previously been assumed to exist, 

 and also, that they are to be found in many localities in which 

 their presence had not been suspected. These views, notwith- 

 standing contradiction at first from certain quarters, are now 

 universally confirmed ; a result to which Reichert, by the dis- 

 covery of a reagent, which readily enables even those who are less 

 practised, easily to isolate the contractile fibre-cells, viz.: nitric 

 and hydrochloric acids of 20 per cent. (Miiller, 'Archiv,' 18 19, 

 and Paulsen, f Obs. Microchem./ 1849) ; and Lehmann, by his 

 chemical investigations upon this tissue, have contributed their 

 share. Contractile fibre-cells occur in all four classes of the 

 Vertebrata, but appear to be wholly wanting in the Invertebrata, 

 since the smooth fibres of these creatures, which have been 



