396 THE ORGANS OF SPECIAL SENSE 



lacrymal sac in the inner angle of the eye. By means 

 of this duet the tears pass from the conjunctiva to 

 the nasal cavity. The mucous membrane lining the 

 walls of the nasal fossae is divided into an olfactory 

 and respiratory portion; in the former the mucous 

 membrane covers the superior turbinated bone and 

 upper part of the septum; it consists of a neuro- 

 epithelium; the respiratory portion is the term given 

 to the remaining portion of the membrane cover- 

 ing the fossa. The membrane lining the nasal cavi- 

 ties is continued through the foramen and fissures 

 leading from it into the sphenoidal and ethmoidal 

 cells, frontal sinuses, antrum of Highmore, and 

 pharynx. 



The entrance to the nasal cavities is called the 

 anterior nares; the back of the nasal cavities open 

 into the pharynx and is called the posterior nares or 

 choanse. 



The End-organs. The end-organs which receive 

 the stimuli that give rise to sensations of odor consist 

 of olfactory and sustentacular cells which rest upon a 

 basement membrane, making up the olfactory portion 

 of the mucous membrane. 



Olfactory sensations are classified into agreeable 

 and disagreeable, depending upon the sensations they 

 create in the individual. 



THE ANATOMY AND PHYSIOLOGY OF THE 



STRUCTURES CONCERNED IN THE 



SENSE OF SIGHT 



The Eye. The eye-ball lies in the fat of the orbit, 

 surrounded by a tunic of fascia, the capsule of Tenon. 

 It is composed of segments of two spheres, an anterior 

 smaller and a posterior larger, the junction of the 

 sclerotic and cornea indicating their limits. It measures 

 one inch transversely and vertically, and somewhat less 



