506 THE HORSE'S POSITION IN THE ANIMAL WORLD 



The present enquiry is to ascertain the structure of those peculiar 

 formations on the legs of the horse ftimily, known as chestnuts, ergots, 

 and bare patches of cuticle, and also of the parts described as plantar and 

 palmar pads in man and certain animals, with the view to placing them 

 in the classes of substance to which they respectively belong. 



Perhaps the most simple way of performing the task will be to 

 classify the several structures at the commencement, and then to show 

 by description and illustration how the classification has been arrived at. 



Proceeding on this plan, the structure classed as horn will include all 

 the growths known as chestnuts, ergots, and bare j^atches of hardened 

 cuticle, notwithstanding the decided variations of form which they present 

 to the naked eye. 



In the next class — " Modified epidermic covering " — must be placed all 

 the varieties of jjlantar and jjalmar pads. 



Taking the chestnuts or ergots of the horse first, Ijoth in the adult 

 and in the foetus near the time of birth, there is no difiiculty in showing 

 that they are horny structures. The sections, both transverse and vertical, 

 exhibited in the following diagrams (fig. 666) and in Plate LXIX place 

 the matter beyond doubt, and it will be interesting to compare the 

 difterent sections with the objects as they appear to the naked eye in 

 fig. 665, A, B, c, D. The bare patches covered with hardened cuticle in 

 the ass, and the similar bare patches in the foetus of the mare, are, as 

 previously stated, both quite distinctly true horny structures developed 

 from a villous membrane, exactly as the perfectly formed horny excrescences 

 (chestnuts) are in the adult. 



After maceration in water in the case of the chestnuts of the ass, and 

 without any preparation in those of tlie foetal horse, or of the foal at birth, 

 the epidermic covering may be stripped off, and with a pocket lens the 

 secreting membrane thus exposed may be seen covered with villi. The 

 thin layer which has been stripped from it may by the same instrument 

 be resolved into a fine plate of horn identical with the horn of the sole. 

 Transverse and vertical sections under the microscope show all the details 

 of the structures, the sudden transition from ordinary skin to the villous 

 secreting membrane and the horny covering on the surface. All these 

 parts are indicated in the figures referred to, which may be taken to 

 represent the minute structure of the organs exhibited in fig. 665, a, b, c, d. 



Sections of the ergot in the horse and in the ass exhibit exactly the 

 same intimate structure. In fact they diff'er only in the size and form 

 of the horny growth. No further proof can be required in support of 

 the statement that chestnuts and ergots, whether they appear as horny 

 excrescences or as bare patches of hardened cuticle, are in their minute 



