12 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 



42. 2ndly. The cartilaginous tissue is composed of 

 nucleated cells, the intercellular spaces being filled with a 

 more compact substance, called the hyaline matter. 



43. 3dly. The osseous or bony tissue, which differs from 

 the cartilaginous tissue, in having the meshes filled with salts 

 of lime, instead of hyaline substance, whence its compact and 

 solid appearance. It contains besides minute, rounded, or star- 

 like points, improperly called bone-corpuscles, which are found 

 to be cavities or canals, sometimes radiated and branched. 



44. 4thly. The muscular tissue, which forms the flesh of 

 animals, is composed of bundles of parallel fibres, which pos- 

 sess the peculiar property of contracting or shortening them- 

 selves, under the influence of the nerves, the muscles under 

 the control of the will, are commonly crossed by very fine lines 

 or wrinkles, but not so in the involuntary muscles. Every one 

 is sufficiently familiar with this tissue, in the form of lean meat. 



45. 5thly, the nervous tissue is of different kinds. In the 

 nerves proper, it is composed of very delicate fibres, which 

 return back at their extremities, and form loops, as shown in 

 figures 12 and 13, representing the primary fibres of the au- 

 ditory nerve from the auditory sac of the pike. The same 

 fibrous structure is found in the white portion of the brain. 

 But the grey substance of the brain is composed of very mi- 

 nute granulations, interspersed with clusters of large cells, as 

 seen in fig. 14. 



46. The tissues above enumerated differ from each other 

 more widely, in proportion as they are examined in animals 

 of a, higher rank. As we descend in the scale of being, the 

 differences become gradually effaced. The soft body of a 

 snail is much more uniform in its composition than the body 

 of a bird, or a quadruped. Indeed, multitudes of animals 

 are known to be composed of nothing but cells in contact with 

 each other. Such is the case with the polyps ; yet they con- 

 tract, secrete, absorb, and reproduce ; and most of the Infuso- 

 ria move freelv, by means of little fringes on their surface, 



/*/ cj 



arising from modified cells. 



47. A no less remarkable uniformity of structure is to 

 be observed in the higher animals, in the earlier periods of 

 their existence, before the body has arrived at its definite form. 

 The head of the adult salmon, for instance, contains not only 

 all the tissues we have mentioned namely, bone, cartilage, 



