32 



The membrana nictitans, or accessory eyelid (haw) , is situated 

 near the internal angle between the lids and the eyeball. This 

 membrane serves as a finger for the removal of foreign bodies 

 from the eye. 



ANATOMY OF THE MOUTH. 



The mouth is an irregularly oval cavity at the commencement 

 of the alimentary canal, containing the organs of taste and the 

 instruments of mastication. It is situated between the jaws, its 

 long diameter following that of the head. It is pierced by two 

 openings — the anterior, for the introduction of food, and the pos- 

 terior, through which the latter passes into the pharynx. It is 

 bounded in front by the lips and laterally by the cheeks; the 

 roof is formed by the hard palate; its floor is occupied by the 

 tongue, while the posterior boundary is the soft palate (velum 

 pendulum palati) , the membranous partition separating it from 

 the pharynx. The mucous membrane, continuous with the skin 

 at the lips, covers the whole free surface of the mouth and its 

 contents, except the teeth. The lips are the organs of touch as 

 well as of prehension. The soft palate is a valvular curtain sus- 

 pended between the mouth and the pharynx, attached above to 

 the palatine arch; the inferior border is free and rests on the 

 floor of the pharynx. It is owing to the great size of this mem.- 

 brane that a horse is unable to breathe through his mouth. 



The tongue is a movable musculo-membranous organ, situated 

 on the floor of the mouth between the branches of the lower 

 jaw. It is the special organ of taste and at the same time assists 

 in mastication. 



ANATOMY OF THE SKIN. 



The skin consists primarily of two parts, the superior, non- 

 vascular (without blood vessels) layer — the cuticle or epidermis, 

 and, second, the deep vascular (with blood vessels) layer' — the 

 corium, dermis, or true skin. 



The epidermis is the outer, scaly covering. The true skin or 

 derma lies immediately below the epidermis, is much thicker, 

 and contains the roots of the hair, sweat glands, which are 

 simple tubes extending from the deeper layers of the skin to the 

 surface of the body, pouring out perspiration which carries vpith 

 it certain waste materials from the system. The evaporation of 

 sweat cools the body and assists in regulating its temperature. 



