At certain points where this membrane leaves the tongue it forms distinct folds, which, from their being constant, have received par ticular names, and which act to a certain ex tent as ligaments orfrena of the tongue, not so much by virtue of their being folds of mucous membrane, as from their containing within their reduplications a certain amount of a more or less unyielding tissue ; in some this tissue is a mixture of white and yellow fibre, in others it is muscle.
Of the first sort are three folds, a middle and two lateral, passing from the base of the tongue to the epiglottis, called the glosso epiglottid folds, of which the central, which is always present, and has been called the pos terior frennum of the tongue, and ficenunz epi glottidis , is much the most considerable (fig. 745. d.): they serve rather to check the move ments of the epiglottis than as lingual liga ments. From the sides of the base of the tongue, passing thence to the soft palate, are seen four more folds, two on each side, which, from their position, have been called the pillars of the fauces. They are formed by the raising of the mucous membrane from the general surface by two muscles: the posterior, the least considerable, by the palato-pharyn geus ; the anterior, more marked, by the palatoglossus. The interval between these two is called the anzygdaloid fossa, from its being occupied by the amygdalm, or tonsils : the anterior pair taken together constitute the constrictor of the fauces, and the narrowing caused by the whole apparatus has received the name of the isthmus faucium. From the basis of these folds being muscular their pro minence is liable to constant variety. But the most considerable of these folds, which is called, par excellence, the frcenum of the tongue (fitenum,frenulum lingua.), is placed beneath the anterior free extremity, which it connects with the lower jaw. It consists of a prolonga tion forwards, beyond the free border of the genioglossi, of the median fibrous lamina, which raises into a prominent fold the mucous membrane passing from the under surface of the anterior part of the tongue to the neigh bouring alveoli of the lower jaw : it forms a strong ligament, and limits the backward movement of the anterior extremity of the tongue. Sometimes an extreme shortness of this ligament is a congenital malformation, preventing the free movement of the organ, and so impairing speech, mastication, &c., as to necessitate the operation known as cutting the tongue.
Before entering into the specialities of the anatomy of the tongue, let us examine its general configuration and external characters, taking its surfaces, extremities, &c., in the order above enunciated.
Superior surface.— On regarding the upper surface of the tongue, we see first that it is divided into two symmetrical portions by a median longitudinal furrow (fig. 745. c.), com mencing at the tip, and extending back about two thirds the length of the organ. It is superficial when present, but in many cases does not exist : it is the representative, in this part, of that median line which symmetrically divides all those organs of animal life that are situated in the middle vertical plane. It is very generally, but very incorrectly, stated* that this furrow terminates posteriorly in the foramen cmcum. The two have no relation ; the one often exists without the other ; and in every case that I have seen, the foramen has been separated from the posterior ter mination of the furrow by the ridge of the circumvallate papilla., sometimes by a long
interval. This median furrow seems partly formed by the action of muscles, and partly by a deficiency of papilla?. Another con spicuous character of the upper surface is, that the roughnesses with which it is covered are arranged in lines (fig. 745.), with a direction obliquely forwards and outwards, so that there is formed in the median line a series of angles pointing backwards. This disposition is seen to affect, more or less, all the structures with which the surface is covered. Thirdly, the upper surface of the tongue is seen to be divisible into a smooth and a rough portion. The smooth, or non papillary portion, occupying nearly the pos terior third, is characterised by smooth nodular rugosities (fig. 745. e), formed by small mu ciparous glands, which are abundantly dis tributed beneath the surface, and occupy the whole space between the papillae and epi glottis : they are smallest and most scattered behind, where they are gradually lost ; larger and more prominent in front, where, from their being disposed in the direction already indicated, they form a prominent V-shaped ridge with the opening directed forwards. Just in front of this, separated by a groove, is another V-shaped ridge, more definite, but less constant in shape, formed by two con verging lines of button-like eminences, each surrounded by a circular raised border of more or less regularity ; these compound organs are the circumvallate papilla' (fig. 745. ff ). At the angle formed by the convergence of their two rows, generally a little behind that angle, is situated .a cul-de-sac of very variable size, which has received the name of foranzen &Fount (le trou borgne, lacune de in langue), and which was formerly regarded as the orifice at which several convergent sali vary ducts terminated* ; these supposed sali vary ducts were:afterwards shown by Duver noy -I- and Haller I. to be merely small veins. Meckel considered that this foramen ccum was nothing but a largely developed calyx of a caliciform papilla, of which the central portion was small, or wanting, or misplaced ; that if the central eminence was well de veloped and in its proper situation, the foramen czecum was wanting, and that it only existed from some of the irregularities above mentioned; an opinion adopted by Cruveilhier, and by Professors Todd and Bowman in this country. Meckel states that he has seen two, one a great way behind the other. I have more than once met with the same appear ance. In these cases the anterior one has always contained a well developed papilla. It can evidently perform no essential office, as it is so often wanting. The whole of the su perior surface of the tongue, in front of the circumvallate papilla, comprising its anterior two thirds, is covered by an investment of coriaceous or filamentous asperities, longest in the central parts, and arranged with the most regularity at the back, where they are dis tributed in lines of more or less distinctness, with a direction obliquely forwards and out wards (fig. 745. i i.). These eminences are seen to be of two sorts ; one of a spheroidal shape, distinguished during life by their red colour, and scattered here and there at the posterior part, edges and tip, these are the fungfornz papillce (fig. 745. h.); the others, occupying the whole of the rest of the sur face, are the conical and filifornz. To the minute consideration of these structures a future part of this article will be devoted.