Chap. IILJ EPITHELIUM. 19 



we have a single-layered, in the latter a stratified epi- 

 thelium. The simple epithelium may be composed of 

 squamous cells, simple squamous or simple pavement 

 epithelium ; or it may be composed of columnar cells, 

 simple columnar epithelium. The stratified epithelium 

 may be stratified pavement, or stratified columnar; 

 in the former case all or the majority of the layers 

 consist of squamous or polyhedral cells, in the latter 

 all cells belong to the columnar kind. Simple 

 squamous epithelium, is that which lines the air 

 cells, certain urinary tubules of the kidney (the looped 

 tubes of Henle, the cortical parts of the collecting 

 tubes), the acini of the milk-gland, the inner surface 

 of the iris and choroid membrane of the eyeball. 

 Simple columnar epithelium is that on the inner 

 surface of the stomach, small and large intestine, 

 uterus, small bronchi, ducts and acini of mucous and 

 salivary glands, of some kidney tubules, &c. Stratified 

 pavement epithelium is that on the epidermis, the 

 epithelium lining the cavity of the mouth, pharynx, 

 and resophagus in man and mammals, the anterior 

 surface of the cornea, &c. 



21. The epidermis (Fig. 14) consists of the fol- 

 lowing layers: (a) Stratum corneum: this is the super- 

 ficial horny layer, and it consists of several layers of 

 horny scales, without any nucleus. The layers, which 

 are separated from one another by narrow clefts con- 

 taining air, are then in process of desquamation. This 

 stratum is thickest on the palm of the hand and 

 fingers, and the sole of the foot, (bj The stratum 

 lucidum, composed of several dense layers of horny 

 scales, in which traces of an exceedingly flattened 

 nucleus may be perceived, (c) Then follow many 

 layers of nucleated cells, forming the stratum or 

 rete Malpighii or rete mucosum. The most super- 

 ficial layer or layers of it are flattened scales, which 

 are characterised by the presence around the nucleus 



