The Morphology of Tissues. 



171 



which is arranged in the form of alternating light and dark 

 bands, concerning the physical explanation of which there is 

 much divergent opinion. These cross striae are not visible in 

 the plain or smooth fibres. The striated fibres of 

 vertebrates are developed in the way shown in Fig. 

 78, the plain fibres, on the other hand, are simply 

 elongated cells (see Fig. 79), in which all but a small 

 portion near the centrally placed nucleus has become 

 muscle substance. The smooth muscle-fibre is more 

 clearly cellular in its adult condition than is the 

 striated fibre. But though there is this difference in the 

 cases selected, it is not of universal applicability, for 

 in the earthworm we have smooth fibres which are 

 developed as are the striated fibres of the vertebrate, 

 the nucleus remaining outside of the fibre ; while, 

 on the other hand, there are striated fibres where the 

 nucleus remains, as it does in the plain fibre of the 

 vertebrate, within. 



The nervous tissues are essentially composed of 

 cells which have, as a rule, many and much-branched 

 processes. The processes are the nerve-fibres which 

 seem to be always outgrowths of the nerve-cells. 



The co7inective tissties do not really form so clearly 

 definable an assemblage as do those already treated 

 of. Their general characters are that they consist of 



1§ 



« 5 



tjc 



Fig. So.— Tendon of Mouse's tail, stained with logwood ; showing chains of 

 cells between the tendon-bundles. 17s diameters. (After Shafer, from 

 Quain's "Anatomy.") 



aggregates of cells in which the typical cellular character is largely 

 lost through the conversion of a larger or smaller portion of 



