THE TONGUE 805 



anterior permanent teeth very nearly corresponds with that which had been 

 occupied by the ten milk-teeth ; the difference in width between the incisors 

 of the two sets being compensated for by the smallness of the bicuspids in 

 comparison with the milk-molars to which they succeed. Lastly, the angle 

 formed by the rarnus and body of the lower jaw differs at different ages ; 

 thus it is obtuse in the infant, approaches nearer to a right angle in the 

 adult, and again becomes somewhat obtuse in old age. (See p. 52.) 



Relation of the blood-vessels and nerves to the tooth. There is no evidence that the 

 blood-vessels send branches into the hard substance. The red stain sometimes 

 observed in the teeth, after death by asphyxia, and the red spots occasionally found 

 in the dentine, are due to the imbibition of blood effused on the surface of the pulp. 

 The dentine formed in young animals fed upon madder is tinged with that colouring 

 matter, but this does not appear to take place when the growth of the tooth is com- 

 pleted. Nevertheless the tubules of the dentine may serve to convey through its 

 substance nutrient fluid poured out by the blood-vessels of the pulp. The teeth are 

 sometimes stained yellow in jaundice. 



According to Czermak the primitive nerve-tubules run into the tooth -pulp in 

 bundles, which are large towards the centre, and small at the periphery. They lose 

 themselves in a plexus at the surface of the pulp. Czermak states that the fibres often 

 divide, but that he has not seen loops frequently, and he is doubtful as to the precise 

 mode of their termination, 



THE TONGUE. 



The tongue is a muscular organ covered with mucous membrane. By its 

 muscular structure it takes part in the processes of mastication and deglu- 

 tition, and in the articulation of speech, while its mucous membrane is 

 endowed with common sensibility and is the seat of the sense of taste. The 

 tongue occupies the concavity of the arch of the lower jaw : posteriorly it is 

 connected with the hyoid bone, and the back part of its dorsum forms the 

 floor of the arch of the fauces ; inferiorly it receives from base to apex the 

 fibres of the genio-glossus muscle, and through the medium of that muscle is 

 attached to the lower jaw. 



A. Mucous MEMBRANE. On the under surface of the tongue the mucous 

 membrane is smooth and thin. It forms a fold in the middle line, called 

 the frcenum lingua, placed in front of the anterior border of the genio-glossi 

 muscles. On each side below, as the mucous membrane passes from the 

 tongue to the inner surface of the gums, it is reflected over the sublingual 

 gland. Not far from the line continued forwards from the frsenum, the 

 ranine vein may be distinctly seen through the mucous membrane, and close 

 to it lies the ranine artery. Further outwards is an elevated line with a 

 fimbriated margin directed outwards, which extends to the tip. The ducts 

 of the right and left submaxillary glands end by papillary orifices placed 

 close together, one on each side of the freenum ; and further back, in the 

 groove between the sides of the tongue and the lower jaw, are found the 

 orifices of the several ducts belonging to the sublingual glands. 



The upper surface or dorsum of the tongue is convex in its general out- 

 line, and is marked along the middle in its whole length by a slight farrow 

 called the raphe, which indicates its bilateral symmetry. About half an 

 inch from the base of the tongue, the raphe often terminates in a depres- 

 sion, closed at the bottom, which is called the foramen ccecum (Morgagui), 

 and in which several mucous glands and follicles open. Three folds, named 

 the glosso-epiglottic folds or frseuula, of which the middle one is the largest 

 (frsenum epiglottidis), pass backwards from the base of the tongue to the 

 epiglottis. The upper surface of the tongue is completely covered with 



