SCALY EPITHELIUM. 



Iv 



rounded or spheroidal in shape (fig. xxii., 1 ), and but little larger than their 

 nuclei ; but more commonly the undermost layer is formed (as shown in 

 fig. xxiii.) of oblong cells, which are placed vertically, and may be larger in 

 size than the round cells which lie immediately over them. Such oblong 

 vertical cells occur in the undermost layer of the epidermis, and similarly in 

 the epithelium of the cornea and of various parts of the mucous membranes. 

 Sometimes they form two or three successive rows. Higher up in the mass 

 the cells are enlarged ; they have a globular or oval figure, and are filled 

 with soft matter ; thv.j>ext become flattened, but still retain their round 

 or oval outline ; then the continued flattening causes their opposite sides to 

 meet and cohere, except where separated by the nucleus, and they are at 

 length converted into thin 



scales, which form the upper- p i(r 



most layers. While they are 

 undergoing this change of 

 figure, their substance becomes 

 more firm and solid, and their 

 chemical nature is more or 

 less altered ; for the cell- 

 membrane of the softer and 

 more deep-seated cells may be 

 dissolved by acetic acid, which 

 is not the case with those 

 nearer the surface. The nu- 

 cleus at first enlarges, as well 

 as the cell, but in a much 



less degree. The scales near the surface overlap a little at their edges, and 

 their figure is very various ; somewhat deeper it is mostly polygonal, and 

 more uniform. 



In various parts, the more superficial and denser layers of the scaly 

 epithelium can be readily separated from the deeper, more recently formed, 

 softer and more opaque part which lies underneath ; so that the latter 

 is often distinguished as the Malpighian or mucous layer (stratum or rete 

 mucosum), although it is now well understood not to be an independent 

 membrane. This point will be again noticed in treating of the skin. 



Fig. XXIII. DIAGRAM OF SECTION OF EPITHE- 

 LIUM, IN WHICH THE UNDEUMOST CELLS ARE 

 OBLONG AND VERTICAL. 



Furrowed and sinnous cells of epithelium. It was long since noticed by Henle 

 that the flattened cells sometimes present a striated appearance and quite recently 

 Max Schultze and Virchow have described cells marked on the surface with parallel 

 ridges and furrows (Rlffzelleii), and others (Stachelzellen) covered with spines, and 

 therefore presenting a fringed or denticulate border (fig. xxiv.). Both varieties have 

 been found in the epithelium of the tongue, lips, and conjunctiva, and in the 

 epidermis ; and in all cases are confined to the deeper or Malpighian layers. Similar 

 cells have been found in epithelial cancer and in cancroid tumours ; and flattened 

 cells, beset with minute spines on their free surface, have recently been noticed (by 

 Broueff and Eberth) in the epithelium covering the inner surface of the cat's 

 amnion. 



In thin vertical sections of the epidermis of the fingers I have seen what appeared 

 to be cells with a deeply serrated outline, in the Malpighian layer, but I have not 

 been able to separate them so as to examine them singly. 



Growth. It must be admitted that the continued production of new cells by which 

 this and other kinds of epithelium are maintained, is not yet thoroughly understood. 

 It was at one time commonly believed that the cells which go through the changes 

 of form and position already described, are formed from nuclei arising by independent 

 formation in a blastema supplied by the subjacent vascular membrane; but it is now 



