TONGUE. 



1149 



worm, &c.) is very complex in its structure : 

 it consists, first, of an investment of mucous 

 membrane, very thin and extensible, covered, 

 apparently, by a single layer of epithelium, 

 and a good deal of bluish-grey pigment, and 

 underlaid by fibrous tissue disposed at right 

 angles, transversely and longitudinally. When 

 the sheath, thus composed, is cut open, it is 

 seen to contain another fibrous sheath, smooth, 

 dense, white, and shining, the proper sheath 

 of the stilet, which it closely invests, and which 

 smoothly glides in it. Between these two 

 sheaths is a cavity which is occupied, first, by 

 a longitudinal muscle on each side (essentially 

 a hyoglossus), a very fine and slender fascicle, 

 which runs the entire length of the tongue, 

 and retracts it \^Jien protruded ; secondly, by 

 a nerve on each side, disposed, when the 

 tongue is retracted, in regular sinuosities, and, 

 when drawn out, about five inches long ; it 

 does not appear to give off* any branches to the 

 muscle, and does not diminish in size as it 

 advances, so that it is probably distributed to 

 the extremity, and is sensitive ; thirdly, by 

 some cellular tissue loosely connecting the 

 mucous investment with the fibrous sheath of 

 the stilet ; fourthly, no doubt, arteries and 

 veins. The proper sheath of the stilet does 

 not contain a canal, but is attached to the 

 surface of the stilet, which glides in it not by 

 its movement on the sheath, but by the move- 

 ment of the parts of the sheath on itself. 

 When the stilet is retracted it is seen to be 

 cylindrical throughout, but as it advances its 

 sheath accumulates on its anterior extremity, 

 and it seems gradually to become club-shaped, 

 so that when the tongue is completely re- 

 tracted the under lip is filled not only* with 

 the extremity of the stilet, but with the sheath 

 accumulated on it. Cuvier has described an 

 annular muscle existing throughout the entire 

 length of the membranous portion, which he 

 describes as the proper muscle of the tongue, 

 and to which he attributes its self-elongation. 

 If such a muscle exists, which I will not posi- 

 tively deny, it would fulfil all the required 

 conditions, and leave nothing to be explained ; 

 but I confess that, after careful microscopical 

 research, I have been unable to find any mus- 

 cular fibres having a transverse or circular dis- 

 position, all being referable to the longitudinal 

 bundles already referred to. Hunter has de- 

 scribed what he considered to be two coils of 

 some firm substance, wound in opposite di- 

 rections, which by their approximation would 

 become straightened, and so lengthen the 

 tongue ; this is an ingenious hypothesis, but 

 no more : there is nothing that will bear such 

 an interpretation. Perrault, in speaking of 

 the lungs of chameleons *, expresses an opi- 

 nion that the tongue is driven, or, as it were, 

 coughed out by the sudden expulsion of the 

 air which the lungs contain. 



The hyoid apparatus consists of the hori- 

 zontal projecting portion the stilet already 

 referred to, and four cornua, two short ante- 

 rior ones, and two long vertical posterior ones 

 (fig. 761. A and B). These parts can move 



* Essais de Physique, t. i ii 



freely on each other, the articulation between 

 the stilet and the greater cornua is particularly 

 free. These cornua ascend, and are suspended 

 loosely behind the jaws ; they are about three 

 quarters of an inch long, and are clothed with 

 the muscles that are attached to them. These 

 muscles are, 1st, the genlohyoid (c. A B and 

 C T .), arising from the inner surface of the 

 syrnphysis menti in contact with its fellow, 

 and inserted into the inferior extremity of the 

 vertical cornua, sending up a slip which is 

 attached to its whole anterior border. 2dly, 

 a distinct, small fasciculus, the cerato-maxillary 

 (/), arising from the inner surface of the lower 

 jaw, and inserted into the apex of the vertical 

 cornua. Sdly, the sternohyoid (g), arising 

 from the inner surface of the sternal extremity 

 of the fourth and fifth rib, and inserted into 

 the junction of the cornua and glossal portion 

 of the hyoid. 4thly, the cerato-sternal (h), 

 more slender and flattened than the last, the 

 antagonist of the cerato-maxillary, arising from 

 the outer surface of the sternal extremity of 

 the second rib, and inserted, just opposite the 

 cerato-maxillary, into the apex of the greater 

 cornua. 5thly, the omo-hyoid (i), inserted with 

 the sterno-hyoid. This complicated arrange- 

 ment of muscles, which I have drawn from na- 

 ture* in fig. 761. A, is the mechanism for 

 the direction and extrinsic propulsion of the 

 tongue ; by it the lower extremities of the 

 greater cornua are drawn forward, and the 

 summits depressed, so that, instead of being 

 vertical, they are horizontal and advanced 

 (B). The advance of the whole tongue 

 thus gained is nearly an inch, and since 

 the muscles that principally effect it, the 

 genio-hyoid (e), are very strong, and the 

 movement quick and forcible, the question 

 may arise Is this projectile movement suf- 

 ficient to send the rest of the tongue forward, 

 and effect its elongation, after the hyoid ap- 

 paratus has come to a stop, in the same 

 manner as the arrow flies from the string of 

 a bow, though the string itself is suddenly 

 arrested ? I think not. I think that some 

 such muscular arrangement as that described 

 by Cuvier must exist ; and possibly, some 

 transverse bundles of fibres of not very cha- 

 racteristic appearance, which, from the absence 

 of transverse striae, I rejected as muscle, might 

 have been of a muscular nature. The retrac- 

 tion of the tongue is easily accounted for ; it 

 is simply drawn back on the stilet by the lon- 

 gitudinal muscles. The use of the stilet appears 

 to be, partly as a support to the tongue when in 

 a state of rest, and partly to direct its move- 

 ments ; for aim is seen to be taken while the 

 tongue is still retracted : the animal first places 

 itself in such a position that its head shall 

 be turned directly to the object to be seized; 

 it then fixes its head still more accurately, then 

 slowly opens its mouth to a sufficient distance 

 to allow the free egress of the tongue ; it then 

 seems to fix it with a sort of tremulous rigid 



* It may be well to state that not only these, but 

 all the figures illustrating this article (with one or 

 two exceptions, which I have acknowledged), are 

 original, and have been drawn by myself from na- 

 ture, so that I can vouch for their correctness. 



