THE SKIN. 69 



ing from disease, the skin becomes tight and unyielding, it 

 cannot be raised, and the animal is declared ' hidebound/ 



The difference in the thickness of the skin of different 

 animals depends in a great measure on the thickness of the 

 coriurn, and we find that it is composed of delicate white 

 and yellow fibres, which interlace each other in every direc- 

 tion, and are packed closely. Blood-vessels and nerves 

 ramify through this bed of interlacing fibres, and the whole 

 structures on the surface are found disposed in eminences or 

 papillse and folds, or rugge, so as to extend the surface over 

 which the cuticle is formed. When the blood-vessels and 

 nerves approach the surface, they are disposed in a horizontal 

 plexus, from which branches pass up perpendicularly into 

 the papillae. Lymphatics also abound in the substance of 

 the skin. 



In the open structure of the deeper layer of skin, clumps 

 of fat, the coiled sweat-glands and hair-follicles are seen. 

 As we approach the surface of the skin, we see principally 

 the densely-packed vessels and fibres of the skin, with the 

 straight slender ducts of the sweat-glands, the ascending hairs, 

 and the sebaceous glands, which open into the hair-follicles. 

 A careful examination, however, indicates also the exis- 

 tence of an abundance of muscular tissue disposed in 

 delicate strips, connected obliquely with the hair-follicles 

 so as to lead to changes in the position of the hair on the 

 surface. 



The glands of the skin merit special attention. They 

 differ considerably in different domestic quadrupeds, and 

 have been carefully studied by Gurlt and Ercolani The 

 observations of the first were made in 1835, and of the 

 second in 1854. 



The glands may be classified under two heads the tubu- 

 lar, which include the sweat-glands and glandular masses in 



