THE SKIN AND ITS DISEASES. 381 



CHAPTER XXI. 



THE SKIN AND ITS DISEASES. 



The skin of the horse resembles in construction that of other animals. It consists 

 of three layers, materially differing in their structure and office. Externally is the 

 CUTICLE — the epidermis or scarf-skin — composed of innumerable thin, transparent 

 scales, and extending over the whole animal. If the scarf-skin is examined by 

 means of a microscope, the existence of scales like those of a fish, is readily detect- 

 ed. In the action of a blister they are raised from the skin beneath in the form of 

 pellucid bladders, and, in some diseases, as in mange, they are thrown off in hard, 

 dry, white scales, numerous layers of which are placed one above another. In 

 every part of the body the scarf-skin is permeated by innumerable pores, some of 

 which permit the passage of the hair — through others the perspirable matter finds 

 a passage — others are perforated by tubes through which various unctuous secre- 

 tions make their escape, while, through a fourth variety, numerous fluids and gases 

 are inhaled. It is destitute of nerves and blood-vessels, and its principal use seems 

 to be to protect the cutis from injury, and to restrain and moderate its occasional mor- 

 bid sensibility. 



There is at all times a singular ciiange taking place in this outer covering of 

 the animal. There is a constant alteration and renewal of every part of it, but it 

 adheres to the true skin through the medium of the pores, and also numerous little 

 eminenr.f^s, or projections, which seem to be prolongations of the nerves of the skin. 

 The cuticle is in itself insensible ; but one of its most important functions is to pro- 

 tect and defend the parts beneath, which are so often exposed to the effects of a mor- 

 bid sensibility. 



Beneath the cuticle is a thin, soft substance, through which the pores and eminences 

 of the true skin pass. It is termed the rete mucosum, from its web-like structure, 

 and its soft mucous consistence. Its office is to cover the minute vessels and nerves 

 in their way from the cutis to the cuticle. It is also connected with the colour of the 

 skin. In horses with white hair the rete mucosum is white; it is brown in those of 

 a brown colour — black in the black, and in patches of different colours with those 

 the hue of whose integument varies. Like the cuticle it is reproduced after abrasion, 

 or other injury. 



The cutis, or true skin, lies beneath the rete mucosum. It is decidedly of a fibrous 

 texture, elastic, but with difficulty lacerated — exceedingly vascular, and highly sen- 

 sitive. It is the substance which is converted into leather when removed from the 

 body, and binds together the different parts of the frame. In some places it does this 

 literally and clings so closely to the substance beneath that it scarcely admits of any 

 motion: this is the case about the f-jrehead and the back, while upon the face, the 

 sides and flanks, it han<TS in loosened folds. In the parts connected with progression 

 it is folded into various duplicatures, that the action of the animal may admit of the 

 least possible obstruction. The cutis is thinnest, and most elastic, on those parts that 

 are least covered with hair, or where the hair is altogether deficient, as the lips, the 

 muzzle, and the inside of the flanks. 



Whatever is the colour of the ret^ mucosum, the true skin is of a pale white; in 

 fact, the cutis has no connection with the colour of the hair. Of its general char- 

 acter, Mr. Percivall gives a very accurate description : — " It appears to consist of 

 a dense substratum of cellular tissue, with which are interwoven fibres of a liga- 

 mentous nature, in such a manner that innumerable areolae, like the meshes of a 

 net, are formed in it. These ?.reolas open, through correspondent pores in the cuti- 

 cle, upon the external surface, and are for the purpose of transmitting thither blood- 

 vessels and absorbents, giving passage to the hair, and lodging the various secretory 

 organs of the skin."* 



Over a great part of the frame lies a singular muscle peculiar to quadrupeds, and 

 more extensive and powerful in the thin-skinned and thin-haired animals, than in 



* Percivall's Anatomy of the Horse, [>.'400. 



