A. ORAL CAVITY, BY E. KLEIN. 499 



The thickness of this layer is least where the hair follicles 

 cease ; from this point it gradually increases, and is thickest 

 at the commencement of the muco-membranous portion. Its 

 surface is beset with very numerous thin and elongated papillae, 

 which are frequently clavate, oblique in direction, and vascular. 



Between the fibrous layer and the submucous tissue of the 

 muco-membranous portion, and near the commencement of the 

 latter, are situated the coronary artery and vein. These give off 

 larger and smaller branches to form a plexus beneath the epithe- 

 lium from which the vessels for the supply of the papillae arise. 



The third part of the lip, the muco-membranous portion, 

 possesses an epithelium that far exceeds in thickness that of 

 the two above-named portions ; but if this be followed over the 

 fold of the lip, it will be found again quickly to diminish. It 

 presents the several layers characteristic of laminated flattened 

 epithelium ; the most superficial layers consisting of flattened 

 tubular cells, with a flattened and for the most part elongated, 

 though occasionally spheroidal, nucleus ; subjacent to these 

 are cells that at first are of greater breadth than depth, but 

 become in the deeper layers more and more polyhedric, till 

 they are finally succeeded in the deepest layers by cells which 

 are arranged in the form of palisades. 



Many of these cells are ribbed, or exhibit thorn-like pro- 

 jections, by virtue of which they are connected with each 

 other by a dentated suture. 



The tissue of the mucous layer is composed of finer and 

 coarser fibres. The former are either united into fasciculi, 

 or run, in the form of fine isolated or paired elastic fibres, 

 sinuously between or in many spiral coils around the decus- 

 sating and plexiform fasciculi. Besides these, broad, highly 

 refractile, strongly looped fibres occur. 



Wherever the fibres of the membrana mucosa pursue any 

 definite general direction, it is horizontal, and directed from 

 one side of the lip to the other. Moreover, numerous fasciculi 

 pierce the muscular layers to reach the subcutaneous tissue of 

 the transitional portion. Near the muscular fasciculi the tis- 

 sue undergoes alteration, becoming less dense, and the mucous 

 membrane passes into submucous tissue. 



The membrana mucosa is beset with conical, usually un- 



