94 HISTOLOGY OF HORN. 



surface of the wall, or still better, the vertical section already 

 mentioned, and examining this under a magnification of 25 to 

 50 diameters, we find a number of straight striae of varying 

 thickness, and usually dark in colour, lying parallel with one 

 another and connected by a more transparent and lighter 

 coloured material. 



Taking a fine section at right angles to the stria tion we 



shall, first, be able to detect with the naked eye the same 



punctated appearance already recognised in the transverse 



e er section from the bearing surface of 



Wwh^W:^^^^tM^^ t:he wall. By holding the section up 



■i''^' Wvtf'^M^?^^^^ ^^ ^^ ^^^'^^ many of the points appear 



ti^?\^^(' A^^'^3>f1^>^^0'i to be mere minute holes — a conclusion 



m\%^^^^ confirmed by the microscope (compare 



te-i^:SS^%^'^.Sll^^'^^ / ^§- ^'^)- Under a low power the sec- 

 fc^lk''^^ ?^/^'*S' tion shows a number of rounded or 



oval holes (a) surrounded by dark, 

 crossed lines, which again are em- 

 'tSoIs"?S£'on,onriS'i bedded in a lighter coloured mate- 



i, iiiter-tubular horn. The dark y\.{\ ('k\ 



specks seen in the section repre- \^/* 



sent masses of pigment. rpj^^ j^^j^^ ^^^ _^ ^^^^^ ^^^.j, SUrrOUud- 



ing tissue correspond in position to the parallel dark striae 

 found in longitudinal sections, hence we conclude the striae of 

 the wall are hollow tubes, which, however, are not always empty 

 but often contain loosely packed cells or broken-down cell pro- 

 ducts. They are, in fact, horn tubes, a more correct term than 

 that of horn fibres, which has also been given them. The 

 lighter horny material surrounding them has been termed inter- 

 tubular or connective horn. 



Examination of the sole and soft horn of the fro^- or 

 periople shows an almost exactly similar appearance. The 

 lower surface of the sole, like the upper, exhibits minute 

 openings. On section in an antero-posterior direction, stria 

 are seen running obliquely from above downwards and forwards, 

 the microscopical examination of which shows them also to be 

 horny tubes, though they differ from those of the middle sheath 

 of the wall in their greater breadth and more oblique direction. 

 Sections of fresh, soft horn (like that of the frog) exhibit very 

 fine striae, which usually take a somewhat wavy course. When, 

 however, soft horn is allowed to soak in water for some time 



