THE ELEMENTARY TISSUES 9 



or of several layers of cells. The cells in modified epithelium are 

 adapted or specialized to meet particular uses, such as glandular 

 and ciliated epithehal cells. The term neuroepithelium is 

 applied to the perceptive apparatus of the special senses which 

 are found in such structures as the taste buds of the tongue, 

 rods and cones of the retina, and in the organ of Corti in the 

 ear. Skin glands, hair, and nails arise from the epidermis. 

 Membranes and glands are the more common adult epithelial 

 tissues. 



Squamous (pavement) epithelium occurs in single layers, 

 simple squamous, and in two or more superimposed layers, 

 stratified squamous epitheHum. The stratified type is more 

 common than the simple squamous type. In sectioned tissue 

 the surface layer is often very much flattened, as in the simple 

 type, while the next layer is irregularly columnar. This 

 arrangement is correlated with nutrition to a great extent, for 

 the deeper columnar (formative) cells are the more recent and 

 the squamous surface cells are senescent and are being ehmi- 

 nated. The outer layer of the cornea is composed of classical 

 stratified squamous epithelium, while the simple type is usually 

 obtained for laboratory use from the outer capsule of the 

 crystalHne lense. 



Columnar epithelium may be simple, consisting of a single 

 layer of tall, or prismoidal cells, as in the lining of the small 

 intestine; stratified, when it is more than one layer of cells 

 thick, as in the luminal walls of the epididymis, vas deferens 

 and trachea. 



Modified epithelium commonly occurs in the lining of the 

 larger respiratory tubes as cilliated stratified collumnar 

 epithelium. 



C. MUSCULAR TISSUE 



(a) Striated (striped, skeletal, voluntary) muscle tissue 

 is characterized by its cells having alternating dark and light 

 bands extending across the diameter of the cell. The term 

 voluntary, although in general use, is misleading when applied 



