So 



EIGHTH LECTURE. 



transversely striated has become further developed. The 

 latter contracts rapidly and energetically, the former slow- 

 ly and sluggishly ; the latter constitutes the voluntary mus- 

 cle, the former the involuntary acting. The heart, with 

 transversely striated involuntary fibres, makes, it is true, an 

 exception. 



Pale, nucleated bands were formerly assumed to be the 

 elements of the smooth muscles (Fig. 74, i). 

 In the year 1847 Koelliker reduced the 

 band into a series of cellular elements, lin- 

 early arranged behind each other, his con- 

 tractile fibre cells. At that time this was 

 an important discovery, a proof of the dis- 

 tinguished observer's sharp-sightedness. 



We perceive these contractile fibre cells 

 at a to h. They are sometimes short, some- 

 times longer, not infrequently immensely 

 long, spindle-shaped structures, 0.0282 to 

 0.2256 mm. and more in length, and of 

 moderate diameter, 0.0074 to 0.0151 mm. 

 The appearance of the membraneless cell 

 body is, as a rule, entirely homogeneous, 

 except when a deposition of fat (It) has 

 taken place within it. An elongated nu- 

 cleus (it is called rod-like) is readily seen. 

 fig. 75.— Two trans- Jt contains one or more nucleoli. Occa- 



versely striated muscular 



nbriite («), with the con- sionallvwe find the nucleus double or in 



nective-tissue bundles [l>). J 



even greater number. 

 Smooth muscles are widely diffused throughout the human 

 body. From the oesophagus till near the end of the rectum 

 they form the long known thick muscular layer, and, besides, 

 a still finer one — the muscularis mucosae — in the tissue of the 

 mucous membrane. Smooth muscles are met with, further- 

 more, in the respiratory apparatus, as in the posterior walls of 

 the trachea, in the circular fibrous membrane of the bronchi 

 and their ramifications. According to many, our tissue is 

 not wanting even in the respiratory vesicles of the lungs, 



