THE PALATE. 151 



branches enter the connective tissue between the primary divisions of 

 the glandular tissue and eventually break up into close capillary networks 

 which surround the individual alveoli, the basement membrane and the 

 endothelium alone separating the blood-stream and the gland-cells. The 

 veins maintain the general path of the arteries. The definite lymphatics 

 are limited to the interlobular tissue, usually accompanying the ducts. 

 The perialveolar clefts between the bundles of the fibrous framework 

 represent the interlobular lymph-channels, which are tributary to the 

 lymphatic vessels between the lobules. The nerves supplying the salivary 

 glands form plexuses within the interlobular tissue and include both 

 medullated and nonmedullated fibres. The latter, destined chiefly for 

 the blood-vessels and gland-tissue, are in part the axones of sympathetic 

 neurones, whose cell-bodies are the ganglion-cells collected in microscopic 

 groups along the walls of the larger ducts. On reaching the alveoli, the 

 nonmedullated fibres form epilemmar plexuses on the outer surface of the 

 basement membrane, from which delicate fibrils pierce the membrane to end 

 as varicose hypolemmar threads between the gland-cells. 



THE PALATE. 



The hard palate forms the roof of the mouth, and is bounded laterally 

 by the alveolar border of the upper jaw. The mucous membrane is united 

 firmly to the periosteum covering the roof-bones by the dense connective 

 tissue of the submucous layer. Near the front border of the area, the 

 mucous membrane is thrown into a series of irregular ridges, the palatal 

 ruga;, over which the secondary papilla of the tunica propria are well 

 marked. On each side of an oval median area, the submucosa is occupied 

 by an almost continuous layer of palatal glands, composed of small groups 

 of mucous alveoli, whose ducts open on the surface as minute scattered 

 orifices. 



The soft palate is essentially a fold of mucous membrane, enclosing 

 muscles, tendinous expansions and glands, continued backwards and down- 

 wards from the hard palate to form the mobile arched partition between 

 the nasal and oral subdivisions of the pharynx. The free border is 

 prolonged in a median conical prominence, the uvula, which breaks the 

 general curve of the border into a double arch. The soft palate includes 

 four general layers, which, from above downwards, are: (i) The pharyngeal 

 mucous membrane, which for some distance above the free edge of the 

 palate corresponds with the oral mucosa in possessing stratified squamous 

 epithelium and a layer of elastic fibres in the deeper margin of the tunica 

 propria. Higher, but at a variable distance from the free border, the mucosa 

 changes and assumes the characteristics of the respiratory mucous mem- 

 brane. (2) The fibro-muscular layer, which comprises a muscular complex 

 formed chiefly by the expansions of the palatopharyngeus, levator and tensor 

 palati muscles. (3) The glandular layer, which is in places 5-6 mm. thick 

 and continuous with the glands of the hard palate. The glands are examples 

 of the pure mucous variety, and so closely set that they form a layer 

 broken only in the mid-line near the hard palate by a fibro-muscular 

 septum. They mostly end near the free border of the palate in the vicinity 

 of the base of the uvula, but some are continued into this projection, almost 

 to its tip, as a cylindrical tract of glands through and about which run 

 the fibres of the azygos uvulae muscle. (4) The oral mucous membrane, 

 which, although strictly belonging for the most part to the oro-pharynx, 



