HISTOLOGY 



147 



form of a syncytium, which means that the cyHndrical cytoplasmic 

 units containing the nuclei are not separated from one another by 

 membranes where they meet at their ends. These units branch 

 and unite in such a way that a network of cells is formed. The 

 fibrillae of cardiac muscle are made up of regions of different density 



Fig. 81. — Contractile tissues. A. Non-striated muscle cells in cross-section. 

 Note that many cells are not cut through the region of the nucleus. B. Iso- 

 lated non-striated muscle cell from wall of digestive tract. C. Cross-section 

 of a voluntary muscle. The striated muscle cells are held together in bundles 

 by fibrous connective tissue. D. Portion of striated muscle cell showing mul- 

 tinucleate condition and cross-striations. It has been injured near its right 

 end in order to show the cell membrane. E. Striated muscle cells showing 

 blood supply. F. Cardiac muscle cells from human heart. 



hr, blood vessel; c, cytoplasm; cm, cell membrane; fc, fibrous connective tissue; mh, 

 muscle bundle; n, nucleus. (.4, JS, C, and £ from drawings by D. F. Robertson; K from 

 Schiifer, "Essentials of Histology," copyright, 1016, by Longmans, Green and Co., reprinted 

 by permission.) 



SO that the cytoplasm presents an irregularly striated appearance. 

 Striated muscle is sometimes known as skeletal muscle because it 

 is attached to the bones and by its contractions produces motion of 

 body parts which are supported by bone (Fig. 81 D and E). Since 

 these muscles are under conscious control they are also termed vol- 

 untary muscles. They are called striated because of the fact that 

 the regions of different density in the fibrillar occur at such regular 



