34 CONNECTIVE TISSUE. 



cells is essential. The protoplasm composing the cilia being thus 

 in direct communication with that of the epithelium, being in fact 

 a prolongation of it, the hyaloplasm can flow in and out without 

 hindrance ; the inflow causing them to straighten, the outflow 

 causing them to resume their original condition, which is curved ; 

 this rapid inflow and outflow produce the characteristic motion. 



External agencies affect this motion as they do that of other 

 protoplasm. Chloroform inhibits it, as do temperatures above 

 40 C. or below C. ; while dilute alkalies favor it. 



Simple Epithelium. When epithelium of either of these 

 varieties is arranged in a single layer it is known as simple epi- 

 thelium. 



Stratified Epithelium (Fig. 21). When the epithelial cells 

 are arranged in many layers they form stratified epithelium, the 

 cells of each layer differing in shape. Thus in the epidermis, the 

 epithelium of which is of this variety, the deepest layer is columnar 

 in character ; next to this is a granular layer of spindle-shaped 

 cells ; then one of closely packed cells ; and, most superficial of all, 

 are several layers of dry, horny scales'. 



Stratified epithelium is also found covering the mucous mem- 

 brane of the mouth, the lower part of the pharynx, the esophagus, 

 vagina, and outer third of the cavity of the cervix uteri, and the 

 conjunctiva. 



Transitional Epithelium. This term is applied to epithe- 

 lium which is arranged in a few layers two, three, or four. The 

 line of demarcation between stratified and transitional epithelium 

 is not very distinct. This variety exists in the ureters and bladder 

 in three layers. The inner layer is composed of cuboidal cells, 

 the next of pear-shaped cells, between the lower elongated ends 

 of which is a third layer of small cells. 



The hair, the nails, and the enamel of the teeth are of an 

 epithelial nature, though in a much modified form. Epithelium 

 is nourished by lymph, and with few rare exceptions is not sup- 

 plied with nerves : such exceptions are the epithelium covering the 

 cornea and that in the deep layers of the epidermis. 



CONNECTIVE TISSUE. 



The term " connective " as applied to this large group of tissues 

 implies that they are concerned in binding the body together into 

 one organic whole, without which the tissues would be disconnected 

 and the body lack the support which these structures afford. The 

 following are the varieties : 1. Areolar ; 2. Adipose ; 3. Retiform ; 

 4. Lymphoid ; 5. Elastic ; 6. Fibrous ; 7. Jelly-lfke ; 8. Cartilage ; 

 9. Bone; 10. Dentin. 



Areolar Tissue. Areolar tissue consists of bundles of fibers 

 presenting a wavy appearance (Fig. 24) running in various direc- 



