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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



one heard at a distance ; thus, a frog croaking in an adjoining room was once 

 mistaken by the writer for a large dog barking outside the building. 



D. CUTANEOUS AND MUSCULAR SENSATIONS. 



General Importance of the Cutaneous and Muscular Sensations. 

 Cutaneous sensations are aroused by the operation of some form of energy on 

 the skin, and they include the sensations of touch) of temperature, and of pain. 

 By muscular sensation is meant the appreciation which we have of the intensity 

 and direction of muscular effort. Closely allied to this sensation is a general 

 sensibility through which we gain a c 



knowledge of the relative position 

 of the parts of our bodies, irrespec- 

 tive of movements. The direction, 

 size, distance, and surface features 

 of external objects are usually made 

 known to us through the sense of 



FIG. 285. Tactile corpuscle 

 within a papilla of the skin of 

 the hand (from Quain, after Ran- 

 vier) : n, n, two nerve-fibres pass- 

 ing to the corpuscle ; a, a, ter- 

 minal varicose ramifications of 

 the axis-cylinder within the cor- 

 puscle. 



FIG. 286. Other tactile corpuscles (from Quain ; A, B, after Meckel ; 

 c, after Fischer) : A, longitudinal section showing the interior trav- 

 ersed by connective-tissue septa derived from the capsule ; the nerve- 

 fibres are cut across. B, transverse section at the point of entrance 

 of a nerve-fibre, showing the axis-cylinder branching ; other fibres 

 cut obliquely, c : 1, entering nerve-fibre, medullated ; 2, 2, the same 

 cut variously within the corpuscle ; 3, 3, clear spaces around the 

 fibres ; 4, 4, nuclei of the transverse and spirally -disposed cells of the 

 corpuscle. 



sight or of hearing. Yet these fundamental facts regarding the things 

 about us do not become a part of knowledge through direct visual and audi- 

 tory perception. Such knowledge is based on complex judgments concern- 

 ing the meaning of auditory and visual phenomena according as they have, in 

 past experience, been interpreted by tactile and muscular perceptions. That is, 

 when reduced to its simplest terms, our most practical and important knowledge 

 of the world is the outgrowth of tactile and muscular perceptions ; by and 

 with them all other sense-perceptions of objects have been corrected and com- 

 pared. Thus, so simple a feat as the estimate of the size of a distant object is 



