42 THE ak:\iy house. 



amount of light admitted through the central opening, which 



is called the pupiJ. The crystalline lens is a small transparent 

 body situated immediately behind the pupil ; it is thick in the 

 center and tapers toward the edges. Its function is to draw 

 the rays of light to a focus on the retina. When the lens is 

 diseased and no light can i^ass through, the animal is said to 

 have a cataract. The eyelids are two movable curtains, superior 

 and inferior, which protect the eye. The memhrana nictltans^ 

 or accessory eyelid (haw), is situated near the inner angle be- 

 tween the lids and the eyeball. This membrane acts like a 

 finger in the removal of foreign bodies from the eye. 



ANATOMY OF THE SKIN". 



The skin consists jDrimarily of two parts: The outer, non- 

 vascular layer, called the cuticle or epiderTnis^ and the deep 

 vascular layer, called the corium, derTnis, or true skin. 



The epidermis is a scaly covering. The true skin or dermis 

 lies immediately under the epidermis, is much thicker, and con- 

 tains the roots of the hair, the sweat glands, and the sebaceous 

 glands. 



Sweat glands are simple tubes extending from the deeper 

 layers of the skin to the surface of the body and pouring out 

 perspiration, which carries with it certain waste materials from 

 the system. The evaporation of sweat cools the body and 

 assists in regulating its temperature. 



Sebaceous glands secrete an oily fluid. On parts of the skin 

 which are subjected to much friction these glands pour their 

 oil directly upon the outer surface, as in the sheath, the back 

 of the pastern joints, etc. Usually, however, the glands open 

 into the hair follicles or sacs, and the oily secretion gives gloss 

 to the hair, prevents it becoming dry and brittle, and keeps the 

 surrounding skin soft and supple. 



ANATOMY AND PHYSIOLOGY OF THE FOOT. 

 (Plate IX.) 



The horse's foot is composed of three parts, viz : The bony 

 framework or skeleton, completed by certain elastic structures 

 of cartilage and fat ; the layer of highly sensitive flesh (quick), 

 which covers the framework ; and, the box or case of horn, 

 called the hoof, which incloses and protects the above-men- 

 tioned structures. 



