232 THE ORGANS 



Fine lymph spaces occur in the papillae and open into a plexus of 

 small lymph capillaries just beneath the papillae. These communi- 

 cate with a deeper plexus of larger lymphatics, wliich increase in size 

 and number as they pass backward and form an especially dense ] 



lymphatic network at the root of the tongue in the region of the 

 lingual tonsils. 



Nerves.— Sympathetic fibres pass mainly to the smooth muscle 

 of the blood-vessels and to the glands. Medullated motor nerve 

 fibres supply the lingual muscles. Medullated sensory nerves in- 

 clude those of the special sense of taste as well as those of ordinary 

 sensation. They end freely among the epithelial cells or in con- 

 nection with special end-organs — the taste buds mainly in the circum- 

 vallate papillae, and the end-hulhs of Krause in the fungiform papillae. 



TECHNIC 



Remove pieces of the dorsum of the tongue, selecting parts that will include 

 the different forms of papillae and cutting well into the underlying muscular 

 tissue. Treat as in technic 2, p. 228, or sections may be stained with haematoxy- 

 lin-picro-acid-fuchsin (technic 3, p. 21). g 



In sections from the back part of the tongue good examples of mucous and 

 serous glands are usually found. 



In small sections of the tongue the muscle fibres are seen arranged in bundles, 

 surrounded by connective tissue and interlacing in all directions. For the stud\^ 

 of the arrangement of the different planes of muscle, complete transverse sec- 

 tions should be made at intervals through the entire tongue. The muscle and 

 connective-tissue relations are best brought out by the haematoxylin-picro-acid- 

 fuchsin stain. 



A tooth is a hard bone-like structure, part of which projects above 

 the surface of the jaw as the crown, while the deeper portion, the root 

 or fang, is buried in a socket of the alveolar margin (Fig. 137). The 

 junction of the root and crown is known as the neck. 



A tooth consists of a soft central core, the pulp cavity, surrounded 

 by dentine (Figs. 137 and 139). The latter constitutes the main bulk 

 of the tooth. The exposed portion of the dentine is covered by a thin 

 layer of extremely hard substance, the enamel (Fig. 137, i), while the 

 alveolar portion of the dentine is covered with cementum (Fig. 137, 3) • 

 Of these the dentine and cementum are of connective- tissue origin, 

 the enamel of epithehal. 



The pulp cavity occupies the central axis of the tooth (Figs. 137 

 and 139). In the root it is known as the root canal. At the apex of 



» 



The Teeth 



'i 



