360 MOHBID ANATOMY OF THE SKIN. 



of these scales is made up of horny cuticular cells is beyond 

 doubt ; some authors indeed allege that they have succeeded in 

 isolating fibres and lamellae, b}^ teazing out the scales after macera- 

 tion ; but these fibres and lamella) must also have consisted of 

 •epidermic cells. The mode of their occurrence will be self- 

 evident from the ensuinp; observations. 



If we break an ichthyotic scale in two, we may detect a 

 vertical striation on the fractured surface ; here and there too, 

 something like stiff fibrils may appear to project. By macerating 

 the scale in feebly alkaline licjuids, and then treating it very 

 cautiously with needles, shaking it, &c., we may now and then 

 succeed in breaking it up entirely into vertical prisms, or, 

 if the term be preferred, into short and thick fibres. Every one 

 of these fibres may be shown to consist of a certain immber of 

 horny lamella) concentrically grouped round a central axis; 

 when cut across, they may be counted on the cut surface like 

 the annual rings of a tree. In the axis of the upper two-thirds 

 of each pseudo-fibre we find nothing: in the lower third we find, 

 either nothing at all, or a minute cavity which was once occupied 

 by a more or less elongated papilla of the cutis. We infer fi'om 

 this, that it is the papilla) which regulate the peculiar stratifica- 

 tion of the horny lamellae. The axis of our concentric cylinder 

 is continuous with that of the papilla ; and the almost vertical 

 inclination of the lamellie is merely a repetition of its steep and 

 sloping sides. 



This explanation does not cover all the phenomena of ich- 

 thyosis. We must bear in mind that the surface of the skin also 

 presents vertical planes where it is bent inwards to form the hair- 

 sacs ; that these vertical surfaces are directly continuous with the 

 sides of the papillae ; also, that the epithelial lining of the hair- 

 sacs is merely a prolongation of the epidermis. Nothing is more 

 usual than the extension of the ichthyosis to the hair-sacs when 

 it happens to affect hairy parts of the skin. The horny lamellae 

 which are thus produced, form, as might liave been anticipated, 

 casts of the hair-sacs ; on transverse section they exhibit con- 

 centric rings round an axial cavity. When the cavity is occu- 

 pied by a hair, this appears in some sort as the axis of the 

 laminated body ; this circumstance may be made use of as a 

 guide ; but it must not lead us to imagine that the hair, as such, 

 exerts any regulating influence upon the stratification of the 



