396 ORGANS OF THE SENSES. 



round a central mass of nerves, form the elements which take 

 the place of the three portions of which the tactile corpuscles 

 of feeling were formerly supposed to consist. The transverse 

 nuclei belong to the sheath of Schwann. 



On the other hand, the corpuscles of Pacini and Yater are 

 found in parts of the organism in which they can be of little 

 use in respect to touch, properly so called : we find them, not 

 only in the mesentery (see above), but also in the nerves 

 which go to the bones, and even in the interior of the 

 muscles. They appear to be extremely sensitive to compres- 

 sion, and their function is, no doubt, connected with this 

 mode of sensibility : for instance, their sensations indicate the 

 degree of contraction of the muscles, according to the com- 

 pression which these muscles produce upon them. They are 

 also subjected to other kinds of pressure: thus the corpuscles 

 situated in the articulating capsules are compressed by the 

 bones in certain movements, and also by the tension of 

 the ligaments ; in the mesentery, they are compressed by the 

 abdominal muscles, acting upon the walls of the viscera; 

 their superficial position, under the integuments, is favorable 

 to the transmission of external pressure (Rauber). 1 



The functions of touch are most highly developed in those 

 parts which contain the largest number of nerves and tactile 

 corpuscles: thus the organs which we chiefly use are the 

 hands, the tongue, and the teeth, riot forgetting the sole of 

 the feet, which is a constant organ of touch during walking, 

 and which, judging of the character of the ground, causes 

 and modifies the reflex action of locomotion, almost without 

 any exercise of the consciousness or of the will (see p. 48). 

 The parts in which the sensation of pressure and of temper- 

 ature reside are not exactly the same, although it is impos- 

 sible to point out the cause of this difference. 



The sensation of temperature is almost generally diffused 

 over the whole surface of the body, and it would seem at first 

 thought as if no part is more privileged in this respect than 



1 The sensation and the measure of contraction of those muscles 

 in which these corpuscles are not found is produced by other special 

 methods of arrangement. This is the case in regard to the muscles 

 of the jaw, and the teeth, the muscles of the eyelids, the conjunc- 

 tiva, etc. A fact which seems to show the independence of the 

 muscular sensations on the sensibility of the skin is, that if this 

 sensibility is diminished by means of cold, the sensations of mus- 

 cular contraction continue or are even increased. (Rauber, Dis- 

 sert., Munich, 1865. See above, pp. 389 and 390.) 



