FIBROUS TISSUES. BASEMENT MEMBRANE. 117 



lions, so that it assumes a stellate form, like that of the cells of the Geranium- 

 petal ; this seems to be the case in regard to the nuclei of the Bone-cells. 

 In other instances it appears to resolve itself into a fasciculus of fibres ; and 

 this is stated by Henle to be the origin of the yellow fibrous tissue. Further, 

 it may separate into a number of distinct fibres, each composed (like those of 

 the Nostoc, Fig. 18,) of a linear aggregation of granules; it seems to be in 

 this manner, that the tubuli of the Dental structure are formed. Lastly, it 

 may disperse itself still more completely into its component granules ; by the 

 reunion of which, certain peculiar vibrating filaments (the so-called Sperma- 

 tozoa) may be formed, possessing motor powers analogous to those of the 

 Oscillatoriae and other corresponding filamentous products of humble Crvpto- 

 gamic vegetation, but destined to perform most important offices in the func- 

 tion of Reproduction. 



134. We have seen that, in the Vegetable structure, the component cells, 

 tubes, woody fibres (or elongated cells), &c., are held together by simple ad- 

 hesion ; a gummy intercellular substance, which answers the purpose of a 

 cement, being often interposed, sometimes in considerable quantity. But in 

 the Animal body, of which the several parts are destined to move with greater 

 or less freedom upon one another, the aggregations of cells that make up its 

 chief part, either in their original or in their metamorphic form, could not be 

 held together in their constantly-varying relative positions, without some in- 

 tervening substance of an altogether different character. It must be capable 

 of resisting tension with considerable firmness and elasticity ; it must admit 

 free movement of the several parts upon one another ; and it must still hold 

 them sufficiently close together to resist any injurious strain upon the deli- 

 cate vessels, nerves, &c., which pass from one to another, as well as to pre- 

 vent any permanent displacement. Now all these offices are performed in a 

 remarkably complete degree, by the Jlreolar Tissue ( 138); the reason of 

 whose restriction to the Animal kingdom is thus evident. And as necessity 

 arises, in certain parts, for tissues which shall exercise a still greater power 

 of resistance to tension, and which shall thus communicate motion (as in the 

 case of Tendons), or shall bind together organs that require to be united (as 

 in the case of Ligaments and Fibrous Membranes), so do we find peculiar 

 tissues developed that shall serve these purposes in the most effectual manner. 

 Hence these tissues also, although not endowed with any properties that are 

 peculiarly animal, are nevertheless restricted to the Animal Kingdom, as 

 completely as are the Muscular and Nervous Tissues, which make up the 

 essential parts of the apparatus of Animal Life. 



135. That all the Animal tissues are in the first instance developed from 

 Cells, was the doctrine put forth by Schwann, who first attempted to gene- 

 ralize on this subject. By subsequent research, however, it has been shown 

 that this statement was too hasty; and that, although many tissues retain their 

 origin cellular type, through the whole of life, and many more are evidently 

 generated from Cells and are subsequently metamorphosed, there are some, 

 in which no other cell-agency can be traced, than that concerned in the pre- 

 paration of the plastic material. This would appear to be the case, in certain 

 forms of the very delicate structureless lamella of membrane, now known 

 under the name of Basement or Primary Membrane, which is found beneath 

 the Epidermis or Epithelium, on all the free surfaces of the body. In many 

 specimens of this membrane, no vestige of cell-structure can be seen ; and it 

 would rather appear to resemble that, of which the walls of the cells are them- 

 selves constituted.* In some instances, it presents a somewhat granular ap- 



* See a Paper by the Author, on the Microscopic Structure of Shells, &c., in the Annals 

 of Natural History, Dec. 1843. The inner layer of the Shells of Mollusca, after treatment 



