26l 



6. — The Eyelashes, which are the tine hairs that are found on the 

 free edges of the eyelids, and are niore abundant on the upper hd than 

 the lower, their purpose being to assist in preventing the entrance of 

 foreign bodies. 



617. The Lachrymal Gland [Plate XXXVI., A. 6.) is situated on 

 the upper portion of the eyeball, and secretes the tears, which keep 

 the front of the eye moist and clear ; the tears pass through the 

 lachrymal duct into the nose. 



618. The Membrana Nictitans, or Haw, {Plate XXX VI., A. 3.), 

 is a cartilaginous structure, situated to the inner side of the eyeball. 

 Its function is to remove foreign bodies, and shield the eye. 



619. The Eyeball is composed of three coats, viz. : — i. — The 

 Sclerotic and Cornea ; 2. — The Choroid and Iris ; and 3.— The 

 Retina. 



620. The Sclerotic coat {Pla'e XXXVI., B. 3. 3.) is a very 

 dense structure, formed of white fibrous tissue ; and to it are attached 

 the muscles which move the eyeball. This coat forms four-fifths of 

 the external tunic. 



621. The Cornea {Plate XXXVI., B. 2.) is that transparent 

 elliptical portion of the external coat, situated in the front of the eye ; 

 it fits into the sclerotic, somewhat similar to the glass in a watch, so 

 forming the remaining fifth of the outer envelope. 



622. The Choroid coat [Plate XXXVI., B. 4., 4.) consists of 

 three layers ; i.e., the external — composed principally of minute veins; 

 middle — a plexus of small arteries ; and the internal — a dark brown 

 pigmentary layer. 



623. The Iris, [Plate XXXVI.,A. 2., 2. and B. 10., 10.), or curtain, 

 is conected with the choroid, and may be of various colourings ; in the 

 horse, it is generally dark brown. Tlie opening in the centre of the 

 iris is called the pupil, and, in horses, is of elliptical shape. The 

 muscular fibres of the iris are arranged in two directions: — circular 



