1176 SURFACE AND SURGICAL ANATOMY. 
As the permanent teeth push their way towards the surface, absorption of the roots 
of the first set takes place, which either fall out of their own accord or are easily 
removed. Loss of the permanent teeth is followed by absorption of the alveolar 
margin of the jaw. The tooth sockets are lined by a thin periosteum, which is 
anatomically continuous with the pulp tissue of the teeth on the one hand and the 
dense fibrous tissue of the deep layer of the gum on the other. 
The upper incisors and canines and the lower bicuspids have cylindrical roots, 
hence in extracting these teeth they should be first loosened by a slight rotatory 
movement; the roots of the lower incisors and canines and of the upper bicuspids 
are flattened, so that they must be loosened by a lateral movement. The roots of 
the wisdom teeth are convergent, generally welded together and curved backwards, 
especially in the lower jaw. The first and second upper molars have three roots 
which are often divergent (Figs. 650 and 651). 
Tongue.—For practical purposes, as well as on developmental and structural 
erounds, it is convenient to divide the tongue imto an anterior two-thirds— 
the oro-glossus, and a posterior third—the pharyngo-glossus (Wingrave), Fig. 640. 
At the junction of the two portions, immediately behind the median cireumvallate 
papilla, is the foramen cecum, which represents the remains of the upper or 
pharyngeal extremity of the thyro-glossal duct. Congenital cysts and fistule which 
develop from unobliterated portions of this duct are always mesial; those arising 
from the upper or lingual portion of the duct are situated between the genlo-hyo- 
elossi, whereas those developed from the lower or thyroid portion are situated 
below the hyoid bone. 
The mucous membrane covering the pharyngo-glossus is much more sensitive 
than that covering the oro-glossus, hence in using a tongue depressor the instru- 
ment should, except under speci ial circumstances, rest only upon the latter region, 
otherwise a retlex arching of the tongue will be set up, which prevents the operator 
from obtaining a satisfactory view of the throat. Scattered over the pharyngo- 
glossus are clusters of lymphoid follicles (lingual tonsils), which appear on the 
surface as a number of nodular umbilicated elevations provided with little erypts 
into which mucous glands open (Fig. 641). The lingual tonsils are lable to 
chronic inflammation and hypertrophy, conditions which are often accompanied by 
a varicose condition of the veins which he immediately beneath the mucous mem- 
brane containing the palato-glossus muscle. To obtain a satisfact ry view of the 
lingual tonsils in the living subject the laryngoscopic mirror must be employed. 
The muscular bundles of the tongue are separated by a quantity of loose con- 
nective tissue, rich in blood-vessels and lymphaties (Fig ig. 644); hence acute in- 
flammatory cedema of the substance of the tongue may be attended with a degree 
of swelling sufficient to obstruct the respiratory passage. 
The main blood-vessels of the tongue run from behind forwards, nearer its 
under than its upper surface ; incisions into the substance of the tongue to reduce 
swelling and tension should, therefore, be made longitudinally upon the dorsum. 
Bleeding from the lingual artery, divided in the substance of the tongue, is 
temporarily arrested by passing the finger behind the base of the tongue and hook- 
ing it well forward, so as to compress the vessel against the inner surface of the 
lower jaw. On account of the very slender anastomosis between the vessels of the 
two halves of the tongue scarcely any bleeding occurs when the organ is split 
mesially. 
Between the tongue and the inner surface of the gums is the alveolo-glossal 
sulcus, crossed in the middle line by the frenum lingue, which passes upwards 
to the under surface of the tongue (Fig. 643). Immediately on either side of the 
lower part of the frenum is the orifice of Wharton’s duct. A little external to the 
frenum the ranine veins are seen lying immediately under the thin mucous mem- 
brane; to the outer side of the veins are the ranine arteries and the lngual nerves, 
both of which he deeper than the veins, and are therefore not visible. 
The mucous membrane at the anterior part of the floor of the alveolo-glossal 
sulcus is thrown into a slight elevation, which overlies, and is caused by, the 
sublingual salivary gland. The duct of the submaxillary gland (Wharton’s duct) 
and the lingual nerve lie beneath and to the inner side of the sublingual gland, 
