CHAPTEK X.— THE OKGANS OF SPECIAL 



SENSE. 



The Eye of the dog differs from that of the horse in 

 several respects interesting from an anatomical point of 

 view. The globe of the eye is almost spherical and 

 the pupil is circular. The retractor muscle consists of 

 four strips and thus is much less largely developed. The 

 cartilago nictitans is much thinner and more membranous. 

 The upper part of the margin of the orbit is ligamentous, 

 not bony. The iris is devoid of corpora nigra, the 

 tapetum lucidum is whitish with a blunt edge, and the 

 retina differs to an extent in histological detail. Un- 

 doubtedly the physiology of the organ in the two animals 

 differs materially in special points, such as refraction, focal 

 distances, and so on. Of diseases and accidents some 

 special forms are seen in the dog. 



A form of Ulceration of the Eyelids which accompanies 

 mange is described by Blaine. It is denoted by obstinate 

 swelling and loss of hair. On examination minute 

 openings are detectable, and in a long-standing case he was 

 compelled to inject nitrate of silver solution into these ; 

 however, generally the disease yields to an ointment of the 

 nitrate of mercury, and prevention of rubbing and scratch- 

 ing the eye with the foot when the eye is " watery," 

 profuse and persistent lachrymation being present. This 

 sometimes depends on entropion, which Braun has success- 

 fully treated by excision of an elliptical portion of skin from 

 the lower eyelid ('Thierarzt. Mittheilungen') . Williams 

 considers ectropion rare in the dog as compared with 

 entropium and always as affecting the lower lid. Entro- 

 pium he finds frequent in pointers and setters. He speaks 

 of trichiasis as frequent in dogs. Careful examination 



