CHAPTER IV. 



THE TISSUE OF THE ORGANIC MUSCLES. 

 BY J. ARNOLD. 



THE constituents of this tissue are fusiform contractile fibres, 

 connective tissue, and cement, with vessels and nerves. 



FORM AND GENERAL CHARACTERISTICS. Fusiform fibres of 

 this tissue are sometimes designated as smooth muscular fibres, 

 or as contractile or muscular fibre cells ; and when examined in 

 an isolated and uncontracted condition, appear as sub-cylindrical 

 fibres, generally with two or more flattened sides, and occasion- 

 ally in the form of flattened oval plates. They for the most 

 part resemble a spindle, being slightly swollen near the centre, 

 and pointed towards each extremity (fig. 31, a); but the thickest 

 part is frequently not quite centrally situated, being nearer to 

 one end than to the other (fig. 31, 6). 



In many instances the extremities of the fibres are not single, 

 but more or less divided, so that processes are given off from 

 one or both poles ; and in accordance with the depth to which 

 the division extends, the length, form, and relative position of 

 these processes vary (fig. 31, c). Thus, when the depth is slight, 

 they are small, short, and more or less parallel to one another ; 

 when, on the other hand, it is considerable, they are long, broad, 

 and diverge from each other almost at right angles. This fork- 

 ing of the muscular fibres occurs especially in those places 

 where the fasciculi are arranged in the form of a network, and 

 may properly be regarded as peculiar to this variety of the 

 tissue. Such fibres, at all events, occur very frequently in the 

 urinary bladder of the frog, at the points of intersection of the 

 fasciculi. 



