A. ORAL CAVITY, BY E. KLEIN. 505 



fasciculi of connective tissue, the fibres of which run in a 

 straight direction. It also contains a not inconsiderable number 

 of finer or coarser closely coiled elastic fibres. In the mucous 

 membrane of the gum, three separate fibrous layers may be dis- 

 tinguished : a. Fasciculi of fibres which run in a horizontal direc- 

 tion from right to left parallel to the surface, and then break up 

 into smaller fasciculi that, after frequently decussating, reunite 

 into coarser bundles ; these predominate on the anterior surface 

 of the alveolar process over the two following sets of fibres. 

 b. Fasciculi which, proceeding from the periosteum of the al- 

 veolus, cohere in large bundles, and immediately again break 

 up in a fan-like manner whilst coursing towards the epithelium, 

 either from before backwards or from behind forwards. On ap- 

 proximating the epithelium, the smaller fasciculi break up into 

 isolated fibres, which, running apparently between the cells, 

 penetrate the deepest epithelial layers, c. Lastly, there are 

 fasciculi which run in a vertical direction from above down- 

 wards, or from below upwards, and in other respects resemble 

 those described under a. 



At the posterior part of the gum of the upper jaw, where 

 this passes into the mucous membrane of the hard palate, all 

 three sets of fibres frequently decussate. 



The nerves of the mucous layer of the gum are not numerous. 

 The mucous membrane of the hard palate presents many 

 differences in structure from that of the gum. The laminated 

 pavement epithelium, which at first is thinner than that on 

 the gum, gradually increases in depth posteriorly. The num- 

 ber of ribbed cells contained in its middle layers varies at 

 different points. The papillae of the mucous membrane pro- 

 jecting into the epithelium are not nearly so numerous at the 

 commencement of the hard palate as on the gums. The me- 

 dian papillae, especially near the foramen incisivum, are fre- 

 quently observed, through tracts of considerable extent, to be 

 indicated only by sparingly distributed slight depressions of 

 the deep surface of the epithelium. Posteriorly the papillae 

 increase somewhat in number and height, although even in 

 some parts of the posterior third of the hard palate they are 

 not much larger than quite anteriorly. 



The mucous layer subjacent to the epithelium is thinnest 



