NORMAL HISTOLOGY. 141 



CHAPTEE XXI. 

 EYE, EAR, AND NOSE. 



The organs of special sense are developed from the epiderm. 

 Their nervous supply is received from the cerebro-spinal system. 

 Only a brief discussion of the eye, ear, and nose is here given. 



THE EYE. 



There are three coats of the eye an external fibrous tunic, a mid- 

 dle vascular tunic, and an inner nervous tunic. 



1. The external coat includes the cornea and sclerotic mem- 

 brane. 



The cornea is composed of five layers (-1) The anterior epithe- 

 lium; (2) the anterior limiting membrane; (3) the substance 

 proper; (4) the posterior limiting membrane; (5) the posterior 

 endothelium. 



The sclerotic membrane, or sclera, resembles the substantia pro- 

 pria of the cornea and consists of two structures (1) bundles of 

 white fibrous tissue; (2) a layer of loose connective tissue, the lam- 

 ina supra choroidea. 



2. The middle tunic comprises the choroid, ciliary body, and iris. 

 The choroid consists of three layers (1) the choroidal stroma, 



containing blood-vessels; (2) the capillary networks; (3) the vit- 

 reous membrane. 



The ciliary body comprises three portions (1) the ciliary ring; 

 (2) the ciliary processes; (3) the ciliary muscles. 



The iris comprises the following structures : (1) The anterior en- 

 dothelium; (2) the anterior boundary layer; (3) the vascular layer; 

 (4) the posterior boundary layer; (5) the pigment layer. 



3. The nervous tunic. This tunic comprises the retina, which 

 consists of ten layers (1) the pigment layer; (2) the layer of rods 

 and cones; (3) the external limiting membrane; (4) the outer nu- 

 clear layer; (5) the outer reticular layer; (6) the inner nuclear 

 layer; (7) the inner reticular layer; (8) the ganglion-cell layer; 

 (9) the nerve fibre layer; (10) the internal limiting membrane. 



