124 



HEALTH AND DISEASE 



the pupils are dilated and sluggish in their contraction. The anterior 

 choroidal veins are large and visible, and the globe is hard and resisting 

 to pressure. The media are quite transparent, but the movements of the 

 animal indicate defective vision. When examined by the ophthalmoscope 

 the surface of the optic disc is found to be more or less concave and pallid, 

 and the veins are remarkably increased in size, while the arteries are 

 diminished. The remedy in these cases consists in the operation of 

 iridectomy, or removal of a portion of the iris. 



12. THE SKIN (INTEGUMENT) AND ITS APPENDAGES 



The external covering of the body, whether of the vegetable or of the 

 animal organism, is familiarly known as the skin, a word of somewhat 



obscure derivation, 

 most probably going 

 back to the Anglo- 

 Saxon. Integument, 

 however, derived from 

 tego, to cover, at once 

 conveys the proper 

 meaning. No one 

 word, however, can 

 express the character 

 of the structures of 

 which the integument 

 is composed, nor the 

 important functions 

 which it is designed 

 to perform. 



In its physiological 

 signification the skin 

 takes its place among the organs of special sense, being largely supplied 

 with nerves which are capable of appreciating the impressions resulting 

 from contact with other bodies, and also impressions of weight and altera- 

 tions of temperature. In describing its structure it is usual to refer to 

 two principal layers, the outer, composed of cells, and called the cuticle 

 or epidermis, and the lower, entitled the derma or chorium or cutis. 



Cuticle. The cells comprising the cuticle are arranged layer upon 

 layer, and derive their nourishment entirely from the secretory vessels of 



Fig. 258. Microscopic Section of the Cuticle or Epidermis 



A, Horny layer. B, c, D, K, Intermediate young round cells, becoming 

 flattened as they approach the surface. K, Derma or Cutis Vera. 



