The keratinized epithelium (EP) of the face is relatively thin and has the general features of thin skin found in other sites. Associated with it are hair follicles (HF) and sebaceous glands (SGl).
Red margin, lip, human, H&E ×120.
The epithelium of the red margin of the lip is much thicker than that of the face. The stratum granulosum is still present; thus, the epithelium is keratinized. The feature that accounts for the coloration of the red margin is the deep penetration of the connective tissue papillae into the  epithelium (arrowheads). The thinness of the epithelium combined with the extensive vascularity of the underlying connective tissue, particularly the extensive venous blood vessels (BV), allows the color of the blood to show through.
Keratinized epithelium, lip, human, H&E ×380.
The circled area in figure on left is shown at higher magnification here. The reddish brown material in the basal cells is the pigment melanin (M), and the dark blue near the surface is the stratum granulosum (SG) with its deep-blue-stained keratohyalin granules.
Red margin, lip, human, H&E ×380.
The sensitivity of the red margin to stimuli such as light touch is due to the presence of an increased number of sensory receptors. In fact, each of the two deep papillae seen in figure on left contains a Meissner’s corpuscle, one of which (MC) is more clearly seen in this figure.
Mucocutaneous junction, lip, human, H&E ×120.
The transition from the keratinized red margin to the fairly thick stratified squamous parakeratinized epithelium of the oral mucosa is evident in this figure. Note how the stratum granulosum suddenly ends. This is more clearly shown at higher magnification in figure on right.
Mucocutaneous junction, lip, human, H&E ×380.
Beyond the site where the stratum granulosum cells disappear, nuclei are seen in the superficial cells up to the surface (arrows). The epithelium is also much thicker at this point and remains so throughout the oral cavity.
PLATE 48 KEY BV, venous blood vessels EP, epithelium HF, hair follicle M, melanin pigment MC, Meissner’s corpuscle OM, oral mucosa SG, stratum granulosum SGl, sebaceous gland arrowheads, connective tissue papillae arrows, nuclei of superficial cells up to surface
The tongue is a muscular organ projecting into the oral cavity from its inferior surface. It is covered with a mucous membrane that consists of stratified squamous epithelium, keratinized in parts, resting on a loose connective tissue. The undersurface of the tongue is relatively uncomplicated. The mucosa of the dorsal surface, however, is modified to form three types of papillae: filiform, fungiform, and circumvallate. The circumvallate papillae form a V-shaped row that divides the tongue into a body and a root; the dorsal surface of the body, i.e., the portion anterior to the circumvallate papillae, contains filiform and fungiform papillae. Parallel ridges bearing taste buds are found on the sides of the tongue and are particularly evident in infants. When sectioned at right angles to their long axis, they appear as papillae and, although not true papillae, are called foliate papillae. The tongue contains both intrinsic and extrinsic voluntary striated muscle. The striated muscles of the tongue are arranged in three inter-weaving planes, with each arrayed at right angles to the other two. This arrangement is unique to the tongue. It provides enormous flexibility and precision in the movements of the tongue that are essential to human speech as well as to its role in digestion and swallowing. The ar-rangement also allows easy identification as lingual muscle.
Dorsal surface, tongue, monkey, H&E ×65; inset ×130.