449 



mucous layer. In acid fuchsine preparations, as shown in fig. 5, a 

 bright red line is to be seen between this horny tissue and the rete, 

 and this, as well as the cornified epitrichial layer, may be traced from 

 the nail edge around the toe and over the sole. On the back of the 

 toe per. con. this thick loose horny tissue is not found , the upper 

 layer of stratum corneum being formed of a few thin, elongated scales. 

 This cornified epitrichial layer of the edge of the nail, extending also 

 to the palmar and plantar surfaces, bears a striking resemblance to 

 the typus A of the stratum corneum of Zander. This writer, as is 

 well known, has lately described two types of horny cells ^), one 

 (typus A) found only on the palms and soles and inner surfaces of 

 the fingers and toes, consisting of cells characterized by a highly re- 

 fractive, homogeneous appearing edge. In the center a clear, round 

 or oval spot, looking like a hole in the tissue, which Zander considers 

 to be the empty nuclear space, can usually be seen. Between the 

 edges and the central cavity, there is a fine network. Everywhere 

 else on the body the stratum corneum belongs to his typus B, being 

 arranged in lamellae and made up of fully horny flat cells. Moreover 

 Zander regards the stratum corneum as present only in places where 

 his typus A is found, i. e. palms and soles chiefly. As it is here that 

 the epitrichial layer is best developed and most persistent, it seems 

 to me possible that Zander's typus A is a reversion to the type of the 

 embryonic outer or epitrichial cells, which undergo a partial keratosis, 

 just as Zander has assumed for his typus A. If this were the case, 

 the homogeneous stratum lucidum, which it is so difficult to account 

 for, would correspond to the outer horny layer of other parts of the 

 body, and the less cornified cells above it to the looser tissue of the 

 epitrichial layer as seen at the edge of the nail. Section stained with 

 acid fuchsine as represented in fig. 5 show the horny layer of the 

 edge of the nail (which I have, I hope, proved is produced by a 

 keratosis of the outer or epitrichial layer), to be made up of cells 

 corresponding with the typus A of Zander, inasmuch as they contain 

 an empty space in the center and broad thickened walls, while between 

 the walls and central spaces, suggestions of the network of Zander 

 may be seen with the immersion system. This type of horny tissue 

 may also be followed from the nail edge over the palmar and plantar 

 surfaces, and comparison of numerous specimens has convinced me that 

 here, too, it is produced by a keratosis of the outer embryonic layer, 



1) Untersuchungen über den Verhornungsprozefs. His und Beaune's 

 Archiv, 1888, I. Heft. 



