SADDLES AND SORE BACKS. 159 



muscles, which il hides from view. It is there for the purpose of additional ^""i^^^^! 

 strength, but it is this layer of material which contributes so considerably diniculties 

 to the surgical difficulties in treating bad backs, as it prevents matter ^acks*^ 

 pointing to the surface while affording it every facility for burrowing in 

 all directions. It is true this point is only of interest to the surgeon, but 

 the horseman would do well to bear in mind that injuries to the back, 

 from the very anatomical arrangements of the part, all tend naturally to 

 get worse instead of better, and are from the beginning complex, slowly 

 healing injuries which cannot be hurried iij their cure. 



Up to this point we have described the bones and muscles of the 

 back, we have now to clothe the part with skin, and deal in an 

 elementary way with the structural peculiarities of the latter. 



There are two skins, an outer composed of scales possessing very skin 

 little sensation and no blood, and an inner which is highly sensitive and of back, 

 full of blood-vessels. There are many other differences between the 

 inner and outer skin, but for our purpose these distinctions are 

 sufficient. 



Owing to the hair and the colour of the skin the blood can rarely be 

 seen in a horse's skin the same as it can in a man's ; but it is there, 

 flushing the parts now more, now less, depending on the temperature and 

 other local conditions. It is only in the pink skin of horses with white 

 heels that the blood-vessels can be seen, giving the part, especially under 

 the influence of exercise, the bright, ruddy appearance seen in the active 

 ■kin of a man at work. The vessels in the skin which carry the blood 

 are hair-like in diameter and innumerable. Their structure is so delicate 

 that very little pressure is sufficient to keep the parts empty, as can be 

 easily demonstrated on one's hand ; the white mark which follows 

 temporary pressure on the back of the hand is due to the minute blood- 

 vessels being emptied of their blood ; as soon as the blood once more enters 

 the white mark disappears. The influence of this question of blood in the 

 skin will later on be fully dealt with. 



The outer or scaly covering of the skin is mainly for the purpose of Friction 

 protection, protects the delicate parts beneath, and as it gets worn away may cause 

 by friction is replaced from below. Ordinarily the production of scales is galls, 

 equal to the wear and tear, but when friction causes wear and tear to 

 predominate over production, injury arises and the sensitive parts 

 beneath are then exposed. A rub to a back, a gall to a shoulder, are 

 illustrations of excess of wear and tear over production, and represent 

 the simplest form of gall. 



The shape of a back depends entirely on the shape of the bones which 

 compose it. Looking again at fig. 25, bearing in mind how deeply the 



