394 THE ORGANS OF SPECIAL SENSE 



skin will only affect the heat spots, and give rise to 

 the sensation of warmth, and the application of a 

 cold one will only influence the cold spots and create 

 a sensation of coldness. The specific physiologic 

 stimuli to the end-organs controlling the temperature 

 sense are termed thermic vibrations. 



The muscle sense is a series of specific sensations 

 arising as a result of the activities of the muscles 

 of the body or its individual parts of which we are 

 conscious. They are called muscle sensations and 

 are evoked in response to nerve impulses developed in 

 the end-organs in the muscles and tendons, and con- 

 veyed by afferent nerves and their connections with 

 nerve cells in the brain. 



By the consciousness of these sensations we are 

 able to perceive (1) the duration and direction of 

 both passive and active movements of the body; (2) 

 to perceive the resistance offered to movements by 

 external bodies; (3) and to perceive the posture of 

 the body or its individual parts. 



THE ANATOMY AND PHYSIOLOGY OF THE 



STRUCTURES CONCERNED IN THE 



SENSE OF SMELL 



The structures essential to the sense of smell are 

 the nasal fossae, the olfactory nerve filaments lying 

 within the mucous membrane, and the olfactory 

 tracts which are collections of nerve fibers formed 

 into large nerve trunks and the latter ending in the 

 nerve cells in the uncinate convolutions of the cere- 

 brum (area of sense of smell). Matter in the gaseous 

 or volatile state is the means whereby the peripheral 

 nerves are stimulated, in which are developed nerve 

 impulses, transmitted to the cortex, where they give 

 rise to sensations of odor. 



