518 HORN. 



in a state of nature, they imprison other parts between 

 them, and lead to the accumulation of masses of firm un- 

 yielding horn, which inflict injury. The unlimited growth 

 of the fibres is beautifully 'illustrated by cases in which 

 the hoof is not worn down owing to an animal's limb being 

 distorted, and the hoof brought to the ground on its side 

 instead of its normal surface of apposition. 



The growth of the wall of a horse's hoof is in every respect 

 similar to the growth of a human nail. We shall quote from 

 Virchow : " If we consider the nail with respect to its pro- 

 per firm substance, its compact body (Nagelblatt), this only 

 grows from behind, and is pushed forward over the surface 

 of the so-called bed of the nail (Nagelbett), but this in its 

 turn also produces a definite quantity of cellular elements, 

 which ar,e to be regarded as the equivalents of an epidermic 

 layer. On making a section through the middle of a nail, 

 we come, most externally, to the layer of nail which has 

 grown from behind, next to the substance which has been 

 secreted by the bed of the nail, then to the rete malpighii, 

 and lastly to the ridges upon which the nail rests. 



" Thus the nail lies in a certain measure loose, and can 

 easily move forwards, pushing itself over a moveable sub- 

 stratum, whilst it is kept in place by the ridges with which 

 its bed is beset. When a section is made transversely through 

 a nail, we see, as already mentioned, essentially the same 

 appearance presented as that offered by the skin, only that a 

 long ridge corresponds to every single papilla seen in ordinary 

 sections of the skin; the undermost _part of the nail has 

 slight indentations corresponding to these ridges, so that, 

 while gliding along over them, it can execute lateral move- 

 ments only within certain limits. In this manner, the body 

 of the nail which grows from behind moves forward over a 

 cushion of loose epidermic substance in grooves which are 



