198 SPECIAL PHYSIOLOGY. 



grooves, by proper muscles, the tongue is rapidly extended, and is again re- 

 tracted by other muscles. In the chameleon, the tongue lies in the interior 

 of a fleshy sheath, composed of circular muscular fibres, by the contraction of 

 which, the tongue is extruded from the mouth, from which position it is again 

 withdrawn into its sheath, by a proper retractor muscle. In the toad, there 

 is a partly similar contrivance ; but the tongue, in a state of rest, is bent 

 backwards upon itself, and is rapidly unfolded forwards, at the same time that 

 it is protruded from the mouth. The suckers, or organs of attachment, found 

 in the remora and similar fish, by which they attach themselves as parasites 

 to the whale, or other marine animals, are also prehensile in their character ; 

 but for purposes of general prehension, fishes must use their very mobile jaws, 

 the fins never acting in that capacity. 



In the soft Mollusca, a prehensile apparatus, by which they hold to foreign 

 bodies, or seize their prey, is frequently present, consisting of tentacula, or 

 arms, which surround the opening of the mouth. In the Cephalopods, these 

 attain their greatest development, being strong muscular organs, provided on 

 their inner or holding surface with numerous discoid, cup-like suckers, the 

 centres of which can be retracted, after they are applied to any foreign body, 

 and so bring atmospheric pressure into exercise upon their margins. The 

 tentacula of other Mollusca and Molluscoida, are much smaller and more 

 delicate organs. 



In the Annulosa, prehension is also accomplished by appendages connected 

 usually with the anterior segments of the body, and forming either claws, as 

 in the Crustaceans, or the various forms of mandibles, or jaws, seen in those 

 creatures, as well as in the Insects, Spiders, and Myriapods. Even in the 

 softer Worms and Leeches, prehensile power, confined to the mouth, is well 

 provided for by special horny, or calcareous teeth. The prehensile power of 

 the Annuloida is either buccal, as in the Entozoa, or suctional, as in some 

 Echinodermata, or is performed by long arms, as in others. 



In the Coelenterata, prehension is accomplished by means of tentacula, situ- 

 ated around the mouth ; sometimes highly numerous, short, and powerful 

 organs, as in the Sea-anemone ; sometimes delicate, elongated, and fringed ten- 

 tacula, as in the Medusae, Beroe, and Hydra. Most of the Coelenterata have 

 their tentacula furnished with the stinging organs already elsewhere men- 

 tioned. 



The Protozoa can scarcely any of them be said to possess prehensile organs. 



Expression and Gesture in Man. 



The chief seat of expression in the human body, is undoubtedly the 

 face; but, it must be quite understood that no part of the body is ex- 

 empt from the liability to undergo movements, which are true mani- 

 festations or expressions of internal emotions. Thus, the respiratory 

 muscles are also excited to contract in crying, sighing, sobbing, and 

 laughter. The hand is firmly closed, and the foot is stamped on the 

 ground, in rage; the whole frame is erect, and the attitude and gestures 

 are firm, under a spirit of defiance ; whilst the knees are bent, and the 

 body droops, under the influence of fear. The teeth, too, are clenched 

 or opened, in passion or in fright, the movements of the jaws neces- 

 sary to produce this effect, being caused by the muscles of mastication, 

 not by the proper facial muscles. But it is these latter, together 

 with the muscles of the eyeballs, which are chiefly and remarkably 

 dominated by the passions or emotions, or by the voluntary imitation 

 of these, in the case of the actor. The precise mode in which the eye- 

 balls are moved in different directions, will be explained in the chapter 

 on the Senses. As regards the muscles which co-operate to produce 

 any special expression in the face, space does not allow us to particu- 



