EXCRETION 



395 



exposed part, and thus form pads for special protection. Such 

 thickening of the outer layer is well seen in the pads on the feet of 

 a dog or cat. The inner cells of the epidermis are provided with 

 more or less pigment or coloring matter. It is to the varying 

 quantity of this pigment that the '' light or dark " complexion 

 is due. The inmost layer of the epidermis is made up of small 

 cells which are constantly dividing to form new cells to take the 

 place of those in the outer layer which are lost. 



Sweat-Duct 



Sebaceous Gland 



Horny layer 

 Pigment layer 



Tactile Organs' 

 Nerve — 

 Blood Vessels - 



Sweat Gland-zS^- 



Fat 



> Epidermia 



' Dermis 



Subcutaneous layer 



Diagram of section of the skin 



The dermis is largely composed of connective tissue filled with 

 a network of blood vessels and nerv^es. This layer contains the 

 sweat glands, some of the most important glands in the body. 

 Other organs connected with the nervous system and called the 

 tactile corpuscles, cause this part of the skin to be sensitive to 

 touch. ' 



Nails. — Nails are a development from the horny layer of the 

 epidermis. Except at the tip, the nail lies directly on the dermis, 

 and gets its pink color from the blood beneath it. Nails grow 

 from a layer of living cells at their roots, part of the inner layer 

 of the epidermis. 



Hairs. — A hair is also an outgrowth of the horny layer, although 

 it is formed in a deep pit or depression in the dermis; this pit is 



