THE MIDDLE SHEATH OF THE WALL. 



81 



sheath begins at the furrow (figs. 44, /, and 48, l) formed by its 

 upper border, which is known anatomically as the " cutigeral 

 sjroove." This 

 o-roove is broad- 

 est in front, be- 

 comincj narrower 

 as it passes back- 

 ward, and accom- 

 modates the co- 

 ronary band. In 

 the neighbour- 

 hood of the bulbs 

 it is reflected 

 downwards and 



forwards, loses its fig. 4S.— a portion of the wall has beeu removed by making verti- 

 cal cuts through the wall of the toe and heel, and a horizontal 

 cut connecting them just above the bearing margin, a, periople ; 

 b, coronary furrow or cutigeral groove, which is seen to become 

 reflected forwards at c, and to form the upper border of the bar ; 

 (/, the middle sheath at the toe, and cV, at the heel ; e, horizontal 

 section of wall just above the bearing surface ; /, laminal sheath ; 

 this is reflected inwards and forwards at / to form part of the 

 bar ; /", free edge of horny lamina, which is continuous with tlie 

 white portion of the middle sheath ; g, horny sole ; h, white line ; 

 i, small horny prominence at the centre of the toe ; k, portion of 

 frog which becomes continuous with the upper margin of the 

 bar ; I, frog stay, dividing the upper groove of the frog into two 

 pai'ts. 



concave shape, — 

 in fact, ceases to 

 be a groove, — 

 and is continued 

 by a slightly con- 

 vex or fiattish 

 strip (fig. 48, c), 

 which indicates the upper border of the bars. Its course is in 

 a forward direction between the horny frog and the continuation 

 of the innermost sheath of the wall, until finally it is lost in 

 the upper surface of the horny sole. 



The floor of the cutigeral groove is closely punctated, the 

 small holes being the openings of funnel-shaped depressions, in 

 which rest the papilke of the coronary band, and which have 

 the general character shown in fig. 53. The holes in the 

 coronary furrow are much larger than those in the perioplic 

 ring. They vary, however, those in tlie lowest third of the 

 furrow being rather larger and less closely packed than those in 

 the upper. Next the laminal (innermost) sheath are one or two 

 rows of still smaller holes. Generally speaking, where the holes 

 are of large size the inner surface of the middle sheath is 

 coloured white, even where the entire wall is dark coloured ; 

 in light-coloured feet this part is distinguished by its still paler 

 tint. The fact can easily be verified on section. This division 

 of the middle sheath into an outer, hard and dark, and an inner, 



F 



