TUE TONGUE. 441 



thinness of the epithelial layer, particularly of the plates, which must 

 always be least permeable, and upon the abundance and superficiality 

 of the vessels and nerves ; and these considerations readily explain why 

 the lips, in which the papilhv are very nnnierous, and nearly reach the 

 surface of the epidermis, possess a more delicate sensibility than the 

 gums ; and why the point of the tongue, whose papillce even project 

 with a thinner covering, is still more sensitive (compare, also, on the 

 import of the axile Corpuscles, § 39). The epithelium is permeable 

 outwards, as well as inwards, and permits of the passage of plasma 

 from the vessels of the mucous membrane into the cavity of the mouth. 

 In this manner, like the epidermis in relation to the cutaneous perspira- 

 tion, it participates in the formation of the mucous fluid, which is 

 yielded, not only by the glands which open into the oral cavity, but 

 also by the whole surface of the mucous membrane. 



B. OF THE TONGUE. 



§ 131. The Tongue is a mass of muscles attached to a particular 

 bone, the os hi/oides, and covered by the mucous membrane of the cavity 

 of the mouth ; its muscular elements, 0"009-0-028 of a line in breadth, 

 are distinguished from those of the external transversely striated mus- 

 cles, only by being interwoven in the most complex manner, so that in 

 the interior of the tongue the lingual muscles cannot be separately 

 demonstrated as such, but only as secondary bundles and fibres. 



The framework of the tongue may be said to be formed by the two 

 genio-glossi, the musculus transversus Imguce, and the fihro-cartilage of 

 the tongue. The latter, which is also called the lingual cartilage (Fig. 

 170, e), is a dense, whitish-yellow, fibrous lamella, placed perpendicu- 

 larly in the middle of the tongue, between the two genio-glo8si. extending 

 through the whole length of the organ, and is not very appropriately 

 named, inasmuch as it is composed of common tendinous or ligamentous 

 tissue. It commences, low down, upon the body of the hyoid bone, in 

 connection with a broad fibrous lamella, memhrana hgpoglossa (Bh^ndin)^ 

 which stretches from the hyoid bone to the root of the tongue, and 

 covers the extremity of the genio-glossiis, very soon attains the level of 

 the musculus transversus, and, upon the anterior third of the tongue, 

 gradually diminishes, as far as its point, where it terminates very low 

 down. Superiorly, the septum Unguce, as this fibrous mass, 0-12 of a 

 line thick, might well be termed, ascends to within l|-2 lines distance 

 from the dorsum of the tongue ; inferiorly, it extends to where the 

 genio-glossi, become lost in the fleshy mass of the tongue, and termi- 

 nates here, not with a defined border, but by passing into the perimy- 

 sium, between the two genio-glossi. On each side of this sep)tum, the 

 genio-glossi spread out, fan-like, into the tongue (Fig. 169, g, 170, g, 

 171,/), so that they occupy the middle of the organ from its point to 



