THE GUMS. 1567 



premaxillary and the maxillary bones, or to the non-union of two parts of the former, supposing 

 that two such parts really exist. The extra incisor may apparently appear on the median side 

 of the first, between the first and second, or between the latter and the canine. To account for 

 this Rosenberg 1 asserts that the typical number is five, as in the opossum, of which the second 

 and fourth are the two persistent ones, and that either the first, third, or fifth may occasionally 

 present itself. Th. Kolliker 2 records a case of right cleft palate in which, besides the four regular 

 incisors, three were found between the cleft and the right canine. As cases of excess of incisors 

 are much more common than of deficiency, the disappearance of the upper lateral one does not 

 seem imminent ; still, there are signs of degeneration. The crown is less square than that of the 

 central, it is occasionally pointed, often unusually small, sometimes not reaching the line of the 

 other crowns. It may be absent, and then a series of cases can be made ranging from those in 

 which the remaining incisor is separated both from its fellow of the other side and from the 

 canine beside it by large gaps to those in which the teeth are regular and continuous. Very 

 rarely one of the lower incisors is wanting, and, according to Rosenberg, either may fail. 



A fourth molar is very uncommon ; but not at all rarely the wisdom-tooth is late in coming 

 through the gum, and occasionally it never does. It seems sometimes to be wanting and often 

 is rudimentary. It has been seen represented by three detached cusps, an apparent confirmation 

 of Rose's views of the homology of the teeth. 



The entire dental series may be unusually large or small. In the former case the face is 

 prognathous, probably as a result of the increase of space required for the teeth. The upper 

 central incisors are occasionally very large without increase in size of the other teeth. The same 

 is true of the molars ; in which case the number of cusps is generally greater, but the converse 

 does not occur when the molars are unusually small. 3 



The points of the canines may project beyond the line of the other teeth and the molars may 

 increase in size from the first to the third. 



Teeth are sometimes remarkably displaced. The superior canines, owing to their high origin 

 in the second dentition, are particularly subject to it. They may appear on the front of the jaw, 

 in the antrum, the nose, or the back of the mouth. The molars, and especially the wisdom-teeth, 

 are also erratic. 



THE GUMS. 



This term is used rather vaguely to indicate the mucous membrane and sub- 

 mucous tissue covering the alveolar processes and closely attached to the necks of 

 the teeth. Whether the neck is entirely surrounded by it varies in different indi- 

 viduals as the teeth are not in all equally close ; as a rule, owing to the ordinary 

 expansion of the crown from the neck, at least a little of the gum is found between 

 the teeth. It is some 3 mm. thick, dense, firmly fastened to the bone, and is neither 

 very vascular nor very sensitive. 



In structure the gums resemble other parts of the oral mucous membrane, con- 

 sisting of the epithelium and the connective-tissue layer. The latter, directly con- 

 tinuous with the periosteum of the alveolar border and the pericementum, is composed 

 of closely fitted bundles of fibrous tissue and beset with numerous papillae. On 

 young teeth the epithelium is prolonged for from .5-1 mm. over the enamel and often 

 for a short additional distance over the cement, ending in an abrupt margin. In the 

 immediate vicinity of the tooth the papillae sometimes exhibit infiltrations of lym- 

 phoid cells. The gums are without glands. The structures sometimes described as 

 such, as the "glands of Serres," consist of nests of epithelial cells derived from the 

 remains of the atrophic embryonal epithelial sheath (page 1563). 



THE PALATE. 



The Hard Palate. The shape and proportions of the hard palate have been 

 discussed with the bones (page 228), so we have here to do only with its mucous 

 covering. This is very firmly fastened to the rough surface of the bones by dense 

 connective tissue which is particularly thick at the sides, doing much to fill up the 

 angle between the roof and the alveolar process. On either side near the front, 

 extending onto the inner surface of the alveolar processes, is a series of raised ridges 

 (Fig. 1325), in the main transverse, although slightly convex anteriorly, the analogues 

 of the palatal ruga of most mammals. They never extend behind the first molar 

 tooth, are numerous and prominent in childhood, but much reduced in middle age, 

 and occasionally wholly lost. 



1 Morphol. Jahrbuch, Bd. xxii., 1895. 



2 Nova Acte des Leopold. Carol. Akad. der Naturforscher, Bd. xliii., 1882. 



3 Magitot : Traite" des Anomalies du Systeme Dentaire, 1887. 



