The gums (Gr. ovxoc, Lat. gingiv,r) resemble in colour and structure the palatine membrane, except that the glandular apparatus is here re duced to mere follicular pores. They cover either surface of the alveolar piocesses of the jaws, intimately connected with the periosteum, and extend a little way beyond the alveoli to rest against the necks of the teeth by a festooned edge. The denticulated processes of this edge are continued across the alveoli between the teeth, by which means the gums on either sur face communicate with each other; between these processes the concave margin of the gum is reflected upon itself to enter the alveoli, lining their inner surface, and closely applied to the fangs of the teeth. (See TEETH.) The palate and gums receive their arterial branches from the internal maxillary and facial arteries, and their nerves from the spheno-palatine or Meckel's ganglion. (See FIFTU PA IR OF NERVES.) The palatine nerves gain the palate through the anterior and posterior palatine fora mina, and course along immediately beneath the periosteum, lodged in grooves, together with the accompanying arteries, upon the inferior surface ofthe palatine processes of the superior maxillary and palate bone. The palatine arch constitutes the septum between the nasal and buccal cavities, and forms the fixed and resist ing surface against which the tongue acts in deglutition and in the articulation of certain sounds ; previous to the irruption of the teeth and after their decay, the g-ums are continued over the alveolar processes, and by their almost cartilaginous hardness supply their place ; they are rendered peculiarly soft and spongy by the influence of mercury and scurvy upon the system.
The velum palati is a soft moveable curtain stretching backwards and downwards into the cavity of the pharynx from the posterior border of the hard palate, but so continuous with it as to exhibit no indication of their union. From its oblique direction the buccal or inferior sur face is also anterior; it is concave, prolongs back wards the roof of the mouth, and presents the median ridge already noticed on the under surface of the hard palate. The nasal or supe rior surface looks upwards and backwards, is smooth, convex, and continuous with the floor of the nasal cavities; these surfaces terminate in a thin border posteriorly, which is prolonged downwards in the middle line to form the uvula. The uvula is of a conical shape, and raries in length and size in different indivi duals ; it is occasionally found to be bifid at its extremity ; it gives rise on either side near its base to two folds of mucous membrane, called the pillars of the lances, which descend diverging towards the sides of the tongue at its back part,leavingbetween them an interval which is in a great measure occupied by the tonsil ; the anterior pillar proceeds from the base of the uvula in front, and arching outwards and down wards terrninates at the side of the tongue a little in advance of the V-shaped ridge of pa ; the two anterior pillars together form what is denominated the anterior arch of the fauces. The posterior pillars constitute in fact the free border of the velum ; they are nearer to each other at their commencement than the anterior, and from this circumstance (although on a plane posterior) can be seen at the same time with the anterior pillars on looking into the mouth ; they spring from the sides of the uvula to take an arched course outwards and downwards and terminate in the sides of the pharynx. The posterior pillars laterally, with
the velum and uvula above and the base of the tongue below, bound the constricted aperture between the cavities of the mouth and pharynx, which is-called the isthmus faucium ; the uvula dropping in the centre gives the superior out line of this opening a double arched form : it is extremely dilatable, and may be contracted nearly to complete closure by the muscular action of its walls ; it is essentially concerned in the act of deglutition. The fossa which is left on either side between the anterior and pos terior pillars is of a triangular shape, narrow above where the pillars approach each other, broader and deeper below as they diverge. The lower part of this will nearly correspond to the angle of the jaw.
Muscles of the velum pa/ati.—These are on each side, the circumflexus or tensor palati and levator palati mollis, which descend from above to be attached to the velum near its upper sur face ; and the palato-glossus and palato-pha ryngeus muscles, which descend from it to the tongue and palate.; lastly there is the central azygos uvul-x muscle.
The circumflexus palati, tensor palati, or the peristaphylinus extemus (pterygo-staphylin. Chauss.) is a flat, thin muscle, lying to the inner side of the internal pterygoid, and with it occupying the pterygoid fossa; it arises by ten dinous and fleshy fibres from the scaphoid de pression situated at the upper part of the inner pterygoid plate, and extending more outwardly, from a part of the external surface of the carti laginous portion of the Eustachian tube. The muscle descends, partly tendinous and partly fleshy, resting against the outer surface of the internal pterygoid plate, but of sufficient breadth to extend beyond its posterior edge, and terminates in a tendon which winds round the hamular process ; it is here retained in its situation by a small ligament and is surrounded by a synovial capsule to facilitate its mdve ments. The tendon now alters its direction, for suddenly expanding into a thin but strong aponeurosis it spreads horizontally forwards and a little upwards to be inserted into the whole of the posterior border of the palatine process of the palate bone and into its posterior nasal spine, uniting with the tendon from the oppo site side in the median line. It is in relation, so far as regards the vertical portion of the muscle, hy its outer surface with the internal pterygoid, and by the inner with the internal pterygoid plate and the superior constrictor muscle of the pharynx. The horizontal tendons of these muscles form a firm aponeurotic ex pansion in the substance of the velum, which, when tightened by the contraction of the ver tical muscular fibres, affords a powerful resisting surface to the upward pressure of the food while being thrust by the tongue through the isthmus.