CELLULAR CONSTITUENTS OF HOEN. 



97 



tubes and inter- tubular horn. The horn tubes are formed, like 

 the inter-tubular horn, from single cells (compare figs. 62, c, 64, 

 and 65). By pressing on the cover-glass, cells may be detached 

 from the horn tubes and are then difficult to distinguish from 

 those forming the inter- tubular horn. 



The same appearance is presented by the horn of the 

 middle sheath of the wall (fig. 59, h), though in this case 

 examination is more difficult, and seldom succeeds without 

 the use of some caustic fiuid. Leisering has, however, made 



Fig. 61.— Horn cells from the 

 perioplic ring, a, young ; 

 b, older cells. 



Fig. 62. — Horn cells from the frog. 

 a, young ; b, older cells ; c, iso- 

 lated horn tube. 



good preparations from macerated young hoofs. The horn 

 tubes which project above the bearing surface of the wall 

 in new-born foals, after the removal of 'the cap which covers 

 the toe until birth, are useful for such demonstrations. The 

 horny laminee, as we have seen, contain no tubes, but may 

 be divided in a similar way into single horny cells. In 

 their case it is not so essential to add an alkali. From the 

 results, then, of microscopical examination it may be concluded 

 that the horny cells are the elements from which the horn is 

 built up. 



The horn tubes, the inter-tubular horn connecting them, and 



G 



