66 MUSCULAR TISSUE. [sect. 30. 



developed during pregnancy, and attain up to | of a line in length, 

 in the vagina, in the cavernous bodies of the external genitals, and 

 in the broad ligaments of the uterus at various places. 



8. In the male sexual orga7is thej^ occur in the clartos, between 

 the tunica vaginalis communis and propria, in the epididymis, the 

 vas deferens, the seminal vesicles, the prostate, around Cowper's 

 glands, and in the corpora cavernosa of the penis. 



9. In the vascular system, smooth muscles are met with in the 

 tunica media of all arteries, especially the smaller ones, in that of 

 most veins, and of the lymphatic vessels, except the finest; further, 

 in lymphatic glands {Heyfelder), and in the external or adventitious 

 coat of many veins. The muscular elements in vessels of middling 

 size are everywhere fusiform fibre-cells ; in the large arteries, on the 

 other hand, they are short plates, often resembling certain forms of 

 pavement epithelium, and in the smallest arteries, oblong, or even 

 roundish cells ; both of which forms are to be regarded as being 

 more undeveloped. 



10. In the eye, smooth muscles form the sphincter and dilator of 

 the pupil and the tensor choroideos. 



11. In the skin, this tissue, besides entering into the formation 

 of the dartos, occurs in the form of small muscles attached to the 

 hair follicles, also in the areola of the nipple, in the nipple itself, 

 and in many sudoriparous and ceruminous glands. 



Formerly, the elements of the smooth muscles were regarded as long bands, 

 containing numerous nuclei, and, like the transversely striped fibres, were con- 

 sidered as arising by the coalescence of many, cells arranged in series. In 

 1847, I showed that this is not the case; but that, on the contrary, the 

 elements of these muscles are only simple, modified cells ; and demonstrated, 

 at the same time, that these contractile fibre-cells occur wherever contractile 

 connective tissue has been assumed to exist, and are also to be met with in 

 other parts where they were not supposed to exist. 



Literature. — Kolliker, Ueber den Ban und die Yerbreitxmg der glatten 

 Muskeln., in the Mittheil. der Naturf. Gesellschajt in Zurich, 1 847, p. 1 8 ; and 

 Zeitschrift fur Wissenschaftl. Zoologie, vol. L, 1849. Lister, in the Micros. 

 Journal, and Trans, of Royal Society of Edinburgh. 



§ 30. Tissue of the Muscular Fibres, or Transversely Striped 

 Muscles. — The elements of this tissue consist essentially of muscular 

 fibres, or muscular primitive bundles, as they are called, each of 

 which represents a bundle, 0004'" to 003'" in thickness, of 

 fine fibrillse, enclosed by a special, homogeneous, delicate, elastic 

 envelope, the sarcolemma. The fibrils are generally regularly 

 nodular, appearing, as it were, to consist of a number of particles 



