ZOOLOGY 



quite different from horns. A corn (Latin cornu, horn) 

 is a horny thickening of the epidermis in response to 

 pressure ; an expression of a tendency which has re- 

 sulted in various useful adaptations, but which in this 

 case is distinctly injurious. 



3. The term " connective tissue" is used in a general 

 sense to include the inner framework of the body, or 

 more specially and accurately to denote the fibrous ma- 

 terial which unites the various cells and groups of cells 

 much as cellulose does in plants. It does not, however, 

 arise from the other body cells, nor is it secreted by 

 them ; it consists of special cells of relatively primitive 

 type, with their secretions, modified to serve mechanical, 

 ends. It is probably because connective tissue cells re- 

 main in a relatively unmodified condition while nerve 

 and muscle cells are becoming exceedingly specialized, 

 that they are capable later on of assuming so many 



different forms and func- 

 tions. They may produce 

 elastic or non-elastic fibers, 



A B 



From Ritchie's "Human Physiology" 



FIG. 3. Connective tissue. In its first 

 stage connective tissue is a group of 

 cells which build around themselves a 

 mass of jelly-like material, as shown 

 in A . This material hardens into the 

 fibers that are seen between the cells 

 in B. All through the body a frame- 

 work of connective tissue runs, holding 

 the cells, organs, and tissues in place. 



From Ritchie's "Human Physiology" 

 FIG. 4. Bone cells. These much-branched 

 cells deposit around themselves bone ma- 

 terial (6), thus building bones to support 

 the body. The bone cells build a net- 

 work of fibers like dense connective tissue 

 and then fill the spaces between the 

 fibers with hard mineral matter, a is a 

 cavity from which the bone cell has been 

 removed. 



