18 NEKVOUS TISSUE. 



primitive bundle is reached, and that is made up of microscopic fibers 

 termed fibrilloe. Each primitive bundle is enveloped in a strong, elas- 

 tic membrane or sheath, called the sarcolemma. When the sarcolem- 

 nia is torn, the fiber divides into thin minute fibrillse, or more rarely 

 breaks into disks, as seen in Fig. 15. Each one of the fibrillae presents 

 dark and light parts alternating regularly with each other, and corre- 

 sponding exactly with the distances of the transverse stria? on the entire 

 fiber itself. 



FIG. 17. 



Striated muscular fiber separating into fibrillfe. Magnified. 



As already indicated on the 17th page, the bundles of fibers mention- 

 ed above are all enveloped in and bound together by connective tissue, 

 which, at the same time, supports all the vessels and nerves of the 

 muscle, and which, in some cases, also extends in the form of a sheath 

 or fascia, over the whole. 



Unstriated muscle consists of elongated band-like fibers, often called 

 fiber-cells, each of which has an elongated nucleus. These fibers are 

 without strife and they have no sarcolemma, and they do not break up 

 into fibrillae. These fibers are most abundant in the hollow viscera, 

 such as the stomach, intestines, bladder, etc.; but they also occur in the 

 arteries, veins, etc. 



Nervous tissue is soft and generally whitish in color. 

 It constitutes the brain, spinal cord, and all the nerves, and 

 is the seat of sensation. 



As already stated, the kinds of animals are exceedingly 

 numerous. The number of kinds is not known, but may 

 be safely estimated as high as a million, or even higher ; 

 the small and microscopic, however, comprise an immense 

 majority of the whole number. 



