28 HAND-BOOK OF PHYSIOLOGY. 



agency assists the progress of the ovum toward the cavity of the uterus. 

 Of the purposes served by cilia in the ventricles of the brain, nothing is 

 known. (For an account of the nature and conditions of ciliary motion, 

 see chapter on Motion.) 



The epithelium of the various glands, and of the whole intestinal 

 tract, has the power of secretion, i.e., of chemically transforming certain 

 materials of the blood; in the case of mucus and saliva this has been 

 proved to involve the transformation of the epithelial cells themselves; 

 the cell-substance of the epithelial cells of the intestine being discharged 

 by the rupture of their envelopes, as mucus. 



Epithelium is likewise concerned in the processes of transudation, dif- 

 fusion, and absorption. 



It is constantly being shed at the free surface, and reproduced in the 

 deeper layers. The various stages of its growth and development can be 

 well seen in a section of any laminated epithelium, such as the epidermis. 



THE CONNECTIVE TISSUES. 



This group of tissues forms the Skeleton with its various connections 

 bones, cartilages, and ligaments and also affords a supporting frame- 

 work and investment to various organs composed of nervous, muscular, 

 and glandular tissue. Its chief function is the mechancial one of sup- 

 port, and for this purpose it is so intimately interwoven with nearly all 

 the textures of the body, that if all other tissues could be removed, and 

 the connective tissues left, we should have a wonderfully exact model of 

 almost every organ and tissue in the body, correct even to the smallest 

 minutiae of structure. 



Classification of Connective Tissues. The chief varieties of 

 connective tissues may be thus classified: 



I. THE FIBROUS CONNECTIVE TISSUES. 



A. Chief Forms. -B. Special Varieties, 



a. Areolar. a. Gelatinous. 



~b. White fibrous. ~b. Adenoid or Retiform. 



c. Elastic. c. Neuroglia. 



d. Adipose. 



II. CARTILAGE. 

 III. BONE. 



All of the varieties of connective tissue are made up of two parts, 

 namely, cells and intercellular substance. 

 Cells. The cells are of two kinds. 

 (a.) Fixed. These are cells of a flattened shape, with branched pro- 



