STRUCTURE OF THE ELEMENTARY TISSUES. 



25 



shape is very variable, and often departs very widely from the typical 

 columnar form. 



(Inhli't-a'U*. Many cylindrical epithelial cells undergo a curious trans- 

 formation, and from the alteration in their shape are termed goblet-cells 

 (Fir. V<. A, c, andB). 



These are never seen in a perfectly fresh specimen: but if such a 

 specimen be watched for some time, little knobs are seen gradually appear- 



FIG. 20. A. Vertical section of a villus of the small intestine of a cat. a. Striated basilar border 

 of the epithelium, b. Columnar epithelium, c. Goblet cells, d. Central lymph-vessel, e. Smooth 

 muscular fibres. /. Adenoid stroma of the villus in which lymph corpuscles lie. B. Goblet cells. 

 (Klein.) 



ing on the free surface of the epithelium, and are finally detached; these 

 consist of the cell-cont3nts which are discharged by the open mouth of 

 the goblet, leaving the nucleus surrounded by the remains of the proto- 

 plasm in its narrow stem. 



Some regard this transformation as a normal process which is continu- 

 ally going on during life, the discharged cell-contents contributing to form 

 mucus, the cells being supposed in many cases to recover their original 

 shape. 



The columnar epithelial cells of the alimentary canal possess a struc- 

 tureless layer on their free surface: such a layer, appearing striated when 

 viewed in section, is termed the "striated basilar border" (Fig. 20, A, a). 



4. Ciliated cells are generally cylindrical (Fig. 21, B), but may be 

 spheroidal or even almost squamous in shape (Fig. 21, A). 



This form of epithelium lines (a.) the whole of the respiratory tract 

 from the larynx to the finest subdivisions of the bronchi, also the lower 

 parts of the nasal passages, and some portions of the generative apparatus 

 in the male (b.) lining the "vasa efferentia" of the testicle, and .their 

 prolongations as far as the lower end of the epididymis; in the female 

 (c. ) commencing about the middle of the neck of the uterus, and extend- 

 ing throughout the uterus and Fallopian tubes to their fimbriated ex- 

 tremities, and even for a short distance on the peritoneal surface of the 

 latter, (d.) The ventricles of the brain and the central canal of the 



