116 MAMMALIA. 



but when perfectly separated, they are seen to be 

 exceedingly slender, and to consist of alternately light 

 and dark portions in regular series. When the fibrillae 

 of the bundles are in close apposition, as in the natu- 

 ral muscle, the dark portions, being in the same lines, 

 by their coincidence form the transverse striae. The 

 bundles into which they are combined are surrounded 

 by a delicate skin or membrane, with a little cellular 

 tissue. 



The structure of muscle may be observed in a piece 

 of ham which has been soaked for a day or two in 

 spirit of wine, the mounted needles being used to pick 

 it to pieces. 



The above-mentioned transversely striated muscu- 

 lar fibre is that found in the voluntary muscles, or 

 those under the influence of the will. But there are 

 other muscles in animals which are involuntary, or 

 not subject to the will; in these the fibrillar structure 

 is absent, the muscular tissue consisting of simple 

 elongated and nucleated cells. 



Cel'lular tissue This fills the interstices between 

 the other tissues and organs of animals, in the 

 same manner that the vegetable parenchyma does 

 those of plants. It is not, however, composed of cells, 

 but of very fine, soft, colourless, and wavy fibres 

 (PL VIII. fig. 20 ), aggregated into bundles, which 

 interlace so as to leave spaces or areolse between 

 them. 



The cellular or areolar tissue may be found in a 

 piece of beef or mutton, in the intervals of the 

 muscular fibres. 



Skin, The skin is composed of cellular tissue, its 

 outer surface presenting a number of projecting blunt 

 points, called papil'lae. It contains a large number 

 of blood-vessels; and when the capillaries are well 

 filled by injection with a coloured composition, it 

 forms a beautiful microscopic object. 



The skin is covered by the epider'mis or cuticle, 



