EPITHELIAL AND ENDOTHELIAL TISSUE. 325 



cristse acousticse, are found the ciliated auditory, and between these the non- 

 ciliated, so-called indifferent epithelia. In Corti's organ within the cochlea 

 there exist the so-called hair-epithelia, which are divided into the inner and 

 outer, the latter being arranged in four continuous rows along the external 

 pillars. In the gustatory buds (Schwalbe, Loven) there are filiform bodies 

 surrounded by covering epithelia; they are found on the epithelial invest- 

 ment of the circumvallate papillae, on the epithelia of the hard and soft pal- 

 ate, and of the posterior surface of the epiglottis. In the olfactory region of 

 the mucosa of the nasal cavity, Max Schultze discovered, in addition to large, 

 columnar, non-ciliated epithelia, interposed delicate nucleated filaments, 

 which, in amphibia and birds, but not in man, have delicate cilia at their 

 external ends. In none of the formations of neuro-epithelium is the ter- 

 mination of the nerve -fibrillse clearly elucidated. 



Pigmented Epithelia and Endotlielia in man are of infrequent occurrence, 

 while in the lower animals they are exceedingly abundant. The pigmented 

 epithelial layer of the human retina is composed of very regular, hexagonal, 

 flat bodies, the central nucleus, as well as the cement-substance, always being 

 without pigment. The amount of the pigment, and also its shade, varies 

 greatly according to the general complexion of the individual. The more 

 blonde this is, the less pigment will be found in the epithelia, and in albinotic 

 persons it is entirely absent. From the inner surface of the epithelial bodies 

 numerous filaments arise, passing between the rods. These filaments are 

 slightly pigmented in man, but in birds, fishes, and amphibia they abound in 

 coloring matter. 



Glands. All the organs of the body properly termed glands 

 are formations of the epithelium. Some authors have given 

 these epithelia the unnecessary name of " parenchyma or 

 enchyma cells. 7 ' The large majority of glands are composed of 

 a single layer of epithelia. In the body of the gland the 

 cuboidal variety is usually found, and in the duct the columnar ; 

 the cuboidal, however, are sometimes so much elongated as to 

 represent the short columnar variety. Several layers of cuboidal 

 epithelia are seen in the sebaceous glands and the prostate of 

 the adult. 



We distinguish two varieties of glands viz.,, the acinous and 

 the tubular. (See Fig. 141.) 



A roundish, pouch-like prolongation of the epithelial layer 

 into the connective tissue forms a simple acinous gland. Exam- 

 ples of this variety are the mucous glands of the oral cavity, the 

 larynx, the trachea, and some of the sebaceous glands. Repeated 

 foldings of the pouch constitute the formations called compound 

 acinous or racemose glands, such as the sebaceous, the lachrymal, 

 the salivary, the lacteal, the prostatic, and other mucous glands 

 f. i., those in the mucosa of the tongue, of the duodenum, of 

 the trachea, and the glands of Cowper and Bartholini. A third 



