THE TONGUE. 
955 
along its middle, except near the tip, is a depression, from which a fold of mucous 
down to the floor of the mouth, and on 
of the 
membrane, the frenulum lingue, passes 
mandible. 
towards the back of the 
short distance from it, the large 
ranine vein is distinctly seen 
through the mucous membrane. 
Further out still are situated two 
indistinct, fringed folds of mucous 
membrane, the plice fimbriate, which 
converge somewhat as they are 
followed forward .towards the tip, 
near which they are lost. 
From the inferior 
the tongue the mucous membrane 
passes across the floor of the mouth 
to the inner surface of the gum, 
with the mucous covering of which 
it becomes continuous. 
The plice fimbriate correspond pretty 
closely to the course of the ranine arteries 
as they run towards the tip ; the arteries, 
however, are deeply placed in the sub- 
stance of the tongue, at a distance of 
3 to 6 mm. from the inferior surface. The 
plicee, which are more distinct at birth 
and in the foetus, are said to correspond to 
the under tongue found in the lemurs. 
The root of the tongue (radix 
linguz) is the portion of the in- 
ferior aspect which is connected by 
muscles and mucous membrane to 
the mandible and hyoid bone. It 
is of very considerable extent, and 
surface of 
side frenulum, and a 
At each 
—— The philtrum 
Apical gland of 
ae tong ue 
Layer of muscle cut 
to show the gland 
‘\__— Plice fimbriate 
=! — Frenulum lingue 
—Wharton’s duct 
—___ Openings of 
Wharton's ducts 
Sublingual gland 
_ Plica sublingualis, 
“with openings of 
ducts of sublingual 
gland 
Fic. 643.—OPpEN MoutH WITH TONGUE RAISED, AND THE 
SUBLINGUAL AND APICAL GLANDS EXPOSED. 
is, with the base, the most fixed 
part of the organ. It is also the 
situation at which the vessels and 
nerves as well as the extrinsic 
muscles enter. 
The sublingual gland of the left side has been laid bare by 
removing the mucous membrane ; to expose the apical 
gland of the right side a thin layer of muscle, in addition 
to the mucous membrane, has been removed. A brauch 
of the lingual nerve is seen running on the inner aspect 
of the gland. The ranine vein is faintly indicated on 
this side also. 
Structure of the Tongue.— 
The tongue is chiefly composed of striped muscular tissue, in connexion with which are 
found a considerable admixture of fine fat and a median septum of connective tissue 
occupying the central part of the organ. In addition, there are vessels, nerves, glands, 
and lymphoid tissue, the whole being covered over by mucous membrane, except at 
the root (Fig. 644). 
The muscular tissue is derived partly from the terminations of the extrinsic muscles 
—namely, the hyoglossus, styloglossus, genioglossus, palatoglossus, and chondroglossus ; 
but also largely from the intrinsic muscles-—namely, the superior lingualis, inferior 
lingualis, the transverse, and the vertical lingual muscles. These are so arranged that 
they form a cortical portion, made up chiefly of longitudinal fibres—derived above from 
the superior lingualis and the hyoglossus, at the sides from the styloglossus, and below 
from the inferior lingualis. This cortex surrounds a central or medullary portion, divided 
into two lateral halves by the septum, and formed in great part by the transverse and 
vertical fibres, and also by the fibres of the genioglossi ascending to the dorsum. The 
muscular fibres derived from these various sources end by being inserted into the deep 
surface of the mucous membrane. 
The detailed description of the extrinsic and intrinsic muscles will be found on 
page 386. 
The septum is a median fibrous partition found in the medullary portion only, and 
easily exposed by separating the two genioglossi on the under surface of the tongue. 
Anteriorly it usually extends to the apex ; whilst posteriorly it grows gradually narrower, 
and expanding transversely at the same time, it passes into a “broad sheet (the 
ia 
