THE HAND THE GREAT ORGAN. 139 



provided for that purpose ; and in many of them we are greatly in- 

 structed by the muscular sense. 



In treating of the external senses generally, it was remarked, that 

 we are capable of judging, by their aid, of impressions made on us by 

 portions of our own body. By the sense of touch we can derive infor- 

 mation regarding its temperature, shape, consistence, &c. An opinion 

 has, indeed, been advanced, that this sense is best adapted for proving 

 our own existence, as every time that two portions of the body come 

 in contact, two impressions are conveyed to the brain, whilst if we 

 touch an extraneous body, there is but one. 



The tact of mucous membranes is extremely delicate. The great 

 sensibility of the lips, tongue, tunica conjunctiva, Schneiderian mem- 

 brane, lining membrane of the trachea and urethra, is familiar to all. 

 Excessive pain is produced in them by the contact of extraneous bodies ; 

 yet, in many cases, they signally exemplify the effect of habit in blunt- 

 ing sensation. The first introduction of a bougie into the urethra 

 generally produces intense irritation ; but after a few repetitions the 

 sensation may become scarcely disagreeable. 



To appreciate accurately the shape and size of objects, it is neces- 

 sary, that they should be embraced by a part of the body, which can 

 examine their surfaces, and be applied to them in every direction. In 

 man, the organ well fitted for this purpose is the hand. This is situate 

 at the free extremity of a long and flexible member, which admits of 

 its being moved in every direction, and renders it not only well adapted 

 for the organ of touch, but for that of prehension. Man alone pos- 

 sesses a true hand; for although other animals have organs of prehen- 

 sion very similar to his, they are much less complete. Aristotle and 

 Galen termed it the instrument of instruments, and its construction 

 was considered worthy of forming the subject of one of the " Bridge- 

 water Treatises" " On the Power, Wisdom, and Goodness of God, as 

 manifested in the Creation," a task assigned to Sir Charles Bell. 



The chief superiority of the hand consists in the size and strength 

 of the thumb, which stands out from the fingers, and can be brought 

 in opposition to them, so as to enable us to grasp bodies, and to execute 

 various mechanical processes under the guidance of the intellect. So 

 important was the thumb esteemed by Albinus, 1 that he called it a 

 lesser hand to assist the larger "manus parva majori adyutrix." 



In addition to the advantages referred to, the hand is furnished with 

 a highly sensible integument. The papillae 

 are largely developed, especially at the ex- Fig. 52. 



tremities of the fingers, where they are ranged 

 in concentric circles, and rest upon a spongy 

 tissue, by many considered to be erectile, and 

 serving as a cushion, and are well supplied 

 with capillary vessels. (See Figs. 33 and 52.) 

 At the posterior extremity of the fingers, 

 are the nails, which support the pulps of the 

 fingers behind ; and render the contact with . 



i i -, ' . ,. rm i Capillary Net- work at margin of 



external bodies more immediate. This happy lips. 



1 De Sceleto, p. 465. 



