TONGUE. 



1143 



while its posterior extremity unlike terrestrial 

 species, is furnished with a strong retractile 

 muscle. In some other marine gasteropoda, 

 as the limpet, a very small portion only of 

 the tongue is included in the head, whilst 

 the rest of it lies folded up in the abdominal 

 cavity, between the intestines and the muscular 

 foot, but perfectly free ; and in some cases it is 

 nearly twice as long as the entire length of 

 the animal. 



Of the uses of this curious apparatus it is 

 difficult to speak with certainty. The short 

 thick tube of the terrestrial gasteropoda ap- 

 pears adapted for the trituration of food pre- 

 paratory to its passing into the oesophagus : 

 these species are furnished with a large, strong, 

 horny plate, fixed in the mouth at the upper 

 part of the head, and, consequently, the 

 flat end of the tongue acts as an under jaw 

 working against this horny plate. It is not 

 easy, however, to imagine that the long nar- 

 row tube of the whelk tribe can be used in 

 the same way for triturating food, though 

 the envelope of strong muscles would fa- 

 vour that idea, while the consideration of 

 the still longer and perfectly free tube of 

 the limpet renders this use of the tongue 

 among the marine gasteropoda still more 

 improbable. It is well known that the 

 Buccinum widatum and its allies use the flat- 

 tened portion of the tongue as a file, with 

 which they bore holes through the shells of 

 other species and then feed upon them, and 

 the muscular apparatus by which this is ef- 

 fected is an admirable piece of mechanism. 

 It consists of a protractor muscle, over the 

 anterior extremity of which the curved por- 

 tion of the tongue is flexed, which, by its 

 self-elongation, probably by intrinsic trans- 

 verse contraction, projects this recurved por- 

 tion of the tongue from the mouth, and 

 keeps it there ; when the tongue is thus pro- 

 truded, the retractor muscle, already alluded 

 to, attached to its posterior blind extremity, 

 contracts rhythmically, and so pulls the re- 

 curved portion with a sawing motion over 

 the extremity of the protractor muscle, which 

 acts as a pulley for it: thus the teeth which 

 cover the outer or free surface of this reflected 

 portion are brought into the relation, with the 

 objects on which they are to act, the most ad- 

 vantageous for filing them away. But this 

 gives us no clue to the determination of the 

 manner in which the tubular part of the 

 tongue is employed, nor am I aware of any 

 probable conjecture having been advanced 

 upon the subject. 



Professor Loven, of Stockholm, has pro- 

 posed a system of classification of gasteropoda 

 founded upon the forms of the tongue-plates 

 and their arrangement ; and it is probable that 

 conchologists will find the suggestion a valu- 

 able one, not so much for the sole foundation 

 of an arrangement as for a check upon classi- 

 fication on other bases.* 



* For much of the above detail I am indebted to 

 Mr. Thomson, of King's College, as well as for the 

 specimens from which the drawings were made. 



Cephalopoda. Hitherto, in the insects 

 among the Articulata, and the gasteropods 

 among the Mollusca, we have only seen in the 

 tongue an instrument for facilitating, mediately 

 or immediately, the prehension of food : in 

 the Cephalopoda we have the first structural 

 indication of the sense of taste, and apparently 

 in a perfection consistent with the high orga- 

 nisation of the animal in other particulars. In 

 both the tetrabranchiate and dibranchiate or- 

 ders of cephalopods we meet with tongues of 

 very similar structure, possessing in both an 

 anterior and posterior soft papillose part, and 

 an intermediate portion invested with a horny 

 lamina, beset with rows of recurved spines. It 

 is hardly possible to help seeing in this dis- 

 tribution of parts the strong analogy it pre- 

 sents to the mammalian tongue, in which the 

 gustatory papillae are situated near the tip and 

 base, while the centre of the clorsum is occu- 

 pied by a rough indusium, subserving the 

 same double office as the spiny lamina of the 

 cephalopod, protecting the organ and facili- 

 tating deglutition. In the Nautilus the tongue 

 is supported by an oblong horny substance, 

 probably analogous to the basis of the hyoid 

 bone, free at its posterior extremity, but em- 

 braced anteriorly by two retrabent muscles 

 which arise from the posterior margins of the 

 lower mandible. The anterior free extremity 

 of the tongue itself is divided into three soft, 

 fleshy, papillar caruncles, of which the central 

 or anterior one is the largest. Behind them 

 the surface is invested with a thin horny 

 plate, on which are set four longitudinal rows 

 of recurved spines, twelve in each row, each 

 spine being about two lines in length. Be- 

 hind this the tongue is again soft and sensory, 

 but the papillae are coarser ; a fleshy fold pro- 

 jects forward from each side of the fauces, 

 likewise covered with papilla?. In the di- 

 branchiate order the papillary structure is less 

 perfectly developed, and the central horny 

 lamina, instead of being in one plane, is bent 

 at right angles into a vertical and horizontal 

 portion, the incurved spines being set only on 

 the vertical part. The rows of spines are 

 seven throughout, but in the Onyc/iotctcthis, as 

 they descend towards the base of the plate, 

 the outer rows merge in those next them to- 

 wards the centre till there are only three rows. 

 The method in which the cephalopods appro- 

 priate their food, by tearing off piecemeal, by 

 means of their strong and sharp mandibles, 

 portions of the prey they have seized and are 

 holding in contact with their mouth, renders 

 the possession of the sense of taste of high 

 importance to them, as the immediate contact 

 of their food prevents their testing its nature 

 by the sense of sight : at the same time, the 

 full enjoyment of this sense is permitted by 

 the nature of their food, its partially commi- 

 nuted condition, and their protracted method 

 of taking it. 



Vertebrata. In the Invertebrata the defini- 

 tion of a tongue depends, with few exceptions, 

 on little more than locality and function the 

 requisitions of a tongue and the possession of 

 an organ of any sort that fulfils those requi- 



4 n 4 



