STRUCTURE OF MUSCLF. 



443 



FIG. 178. 



together and form commonly a dense mass or sheet. Sometimes 

 they branch more or less regularly, and then are arranged in 

 networks. 



These cells vary greatly in size as well as in the relation of 

 their length to their width, in some places deserving the name 

 fibres, or fibre cells, and in others being only elongated cells. 



The striated muscle tissue is that which is found in the volun- 

 tary skeletal muscles and in the tissue of the heart, and therefore 

 forms the large proportion of the ani- 

 mal, and is known as the flesh. The 

 flesh can by judicious dissection easily 

 be divided into single parts called 

 muscles, each of which contains many 

 other tissues, and is so attached as to 

 carry on certain movements, and may, 

 therefore, be regarded as an organ. 



Such a muscle is inclosed in a sheath 

 of connective tissue, from which sheet- 

 like partitions or septa pass into the 

 mass of the muscle and divide it into 

 bundles of fibres, which they inclose. 

 These septa also act as the bed in 

 which the vessels and nerves lie. 



The bundles of fibres of skeletal Short, striated cells of the heart 

 muscle Vary much in size, giving a uscle separated, one showing the 



B truncated (a), or divided (c) ends, 



coarse or fine gram in different mus- and branches (6). 

 cles ; they are composed of a greater 



or less number of fibres, which lying side by side run parallel 

 one to the other. The single fibres of striated muscle vary in 

 length, sometimes reaching 4-5 cm. (2 inches), but being on an 

 average much shorter, so that they only extend the entire length 

 of a muscle in the case of very short muscles. In long muscles 

 their tapering points are made to correspond with those of other 

 fibres to which they are firmly attached. The soft fibres are 

 pressed by juxtaposition into prismatic forms, so that in a fresh 

 condition they appear polygonal in transverse section. When 

 freed from all pressure or traction they become cylindrical and 



