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"Skull of lizard with Acrodont Dentition. One of those lizards which have the edge of the jaw, without bony aveoli on either the inner or the outer side."-Whitney, 1902

Acrodont

"Skull of lizard with Acrodont Dentition. One of those lizards which have the edge of the jaw, without…

Alimentary canal of a bird. Labels: a, ingluvies; b, proventriculus; c, pancreas; d, duodenum; e, liver; f, biliary cyst and duct; g, pancreatic duct; h, intestice; i, the to caeca; k, rectum; l, right ureter; m, oviduct; n, its aperture in cloaca; o, opening of cloaca.

Alimentary Canal of a Bird

Alimentary canal of a bird. Labels: a, ingluvies; b, proventriculus; c, pancreas; d, duodenum; e, liver;…

The alveolar process and teeth were ground off until the antrum of highmore was well exposed; its anterior wall was removed.

Antrum of Highmore with Roots of Teeth

The alveolar process and teeth were ground off until the antrum of highmore was well exposed; its anterior…

The side view and base of the skull of an ape.

Ape Skull

The side view and base of the skull of an ape.

Archaeopteryx, sometimes referred to by its German name Urvogel ("original bird" or "first bird"), is the earliest and most primitive bird known. Archaeopteryx lived in the late Jurassic Period around 155–150 million years ago, in what is now southern Germany during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now.

Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel ("original bird" or "first bird"), is…

Close-up illustration of scalpriform incisor of a beaver. It is "chisel-shaped; having the character of a chisel-tooth; truncate at the end and beveled there to a sharp edge; specifically said of the incisor teeth of rodents, and the similar teeth of a few other mammals." —Whitney, 1889

Scalpriform, Left Lower Incisor of a Beaver

Close-up illustration of scalpriform incisor of a beaver. It is "chisel-shaped; having the character…

"A, B, C, tunnelings of the carpenter bee; E, the carpenter bee; D, a partition; F, teeth, magnified" — Goodrich, 1859

Carpenter Bee

"A, B, C, tunnelings of the carpenter bee; E, the carpenter bee; D, a partition; F, teeth, magnified"…

"Skull and teeth of Bennett's Kangaroo (Macropus bennettii). i1, i2, i3, first second and third upper incisors; pm, second or posterior premolar (the first having been already shed); m1, m2, m3, m4, the four true molars. The last, not fully developed, is nearly concealed by the ascending ramus of the jaw." —The Encyclopedia Britannica, 1910

Bennett's Kangaroo

"Skull and teeth of Bennett's Kangaroo (Macropus bennettii). i1, i2, i3, first second and third upper…

This illustration shows an example of a bevel gear.

Bevel (gear)

This illustration shows an example of a bevel gear.

Biscupid tooth seen from its outer side; the inner cusp is accordingly not visible.

Bicuspid Tooth

Biscupid tooth seen from its outer side; the inner cusp is accordingly not visible.

Canine Tooth (Eye Tooth).

Canine Tooth

Canine Tooth (Eye Tooth).

Vertical section of canine tooth to illustrate the various parts and structures.

Structure of Canine Tooth

Vertical section of canine tooth to illustrate the various parts and structures.

Sagittal section of canine tooth in situ.

Sagittal Section of Canine

Sagittal section of canine tooth in situ.

Canine teeth of left side, labiial (A) and lateral (B) aspects. C, temporary canines.

Temporary Canine

Canine teeth of left side, labiial (A) and lateral (B) aspects. C, temporary canines.

Transverse section of root of lower canine tooth.

Transverse Section of Root of Canine

Transverse section of root of lower canine tooth.

"Upper Sectorial Teeth of Carnivora. I, Felis; II, Canis; III, Ursus, 1, anterior, 2, middle, and 3, posterior in position, and without distinct root, characteristic of the Ursidae." —The Encyclopedia Britannica, 1903

Carnivora

"Upper Sectorial Teeth of Carnivora. I, Felis; II, Canis; III, Ursus, 1, anterior, 2, middle, and 3,…

The teeth of a carnivorous animal that lives on flesh alone. The front teeth are tearing ones, while the back teeth have sharp edges for cutting. The flesh is first torn by the front teeth, and then it is cut up by the back ones.

Carnivorous Skeleton

The teeth of a carnivorous animal that lives on flesh alone. The front teeth are tearing ones, while…

"The metal cut away near the center reduces the weight and provides passages for air circulation." — Hawkins, 1917

Solid core disk

"The metal cut away near the center reduces the weight and provides passages for air circulation." —…

"Side view of built up armature core. The sheet metal ring sections containing the teeth are fastened into dovetail notches in the spider as shown." — Hawkins, 1917

Armature core

"Side view of built up armature core. The sheet metal ring sections containing the teeth are fastened…

The skull of a crocodile with visible teeth.

Crocodile Skull

The skull of a crocodile with visible teeth.

A wheel with cogs or teeth at right angles to its plane.

Crown-wheel

A wheel with cogs or teeth at right angles to its plane.

Vertical transverse section of the dental sac and pulp of a kitten. Labels: a, dental papilla or pulp; b, the cap of dentine formed upon the summit; c, its covering of enamel; d, inner layer of epithelium of the enamel organ; e, gelatinous tissue; f, outer epithelial layer of the enamel organ; g, inner layer, and h, outer layer of dental sac.

Dental Sac and Pulp

Vertical transverse section of the dental sac and pulp of a kitten. Labels: a, dental papilla or pulp;…

Section of a portion of the dentine and cement from the middle of the root of an incisor tooth. Labels: a, dental tubuli ramifying and terminating, some of them in the interglobular spaces b and c, which somewhat resemble bone lacunae; d, inner layer of the cement with numerous closely set canaliculi; e, outer later of cement; f, lacunae; g, canaliculi.

Dentine and Cement

Section of a portion of the dentine and cement from the middle of the root of an incisor tooth. Labels:…

Part of section of developing tooth of a young rat, showing the mode of deposition of the dentine. Labels: a, outer layer of fully formed dentine; b, uncalcified matrix with one or two nodules of calcareous matter near the calcified parts; c, odontoblasts sending processes into the dentine; d, pulp; e, fusiform or wedge-shape cells found between odontoblasts; f, stellate cells of pulp in fibrous connective tissue. The section is stained in carmine, which colors the uncalcified matrix, but not the calcified part.

Deposition of Dentine

Part of section of developing tooth of a young rat, showing the mode of deposition of the dentine. Labels:…

"Upper and lower teeth of one side of the mouth of a dolphin, as an example of homodont type of dentition. The bone covering the outer side of the roots of the teeth has been removed to show the simple character." —The Encyclopedia Britannica, 1903

Dolphin Teeth

"Upper and lower teeth of one side of the mouth of a dolphin, as an example of homodont type of dentition.…

Enamel fibers. A, fragments and single fibers of the transversely striated enamel, isolated by the action of hydrochloric acid. B, surface of a small fragment of enamel, showing the hexagonal ends of the fibers with the darker centers, or not so high calcified.

Enamel Fibers

Enamel fibers. A, fragments and single fibers of the transversely striated enamel, isolated by the action…

Enamel prisms. A, Fragments and single fibers of the enamel isolated by the action of hydrochloric acid; B, Surface of a small fragment of enamel, showing the hexagonal ends of the fibers.

Enamel Prisms

Enamel prisms. A, Fragments and single fibers of the enamel isolated by the action of hydrochloric acid;…

Longitudinal section of enamel, treated with acid, showing disposition of ranges of enamel prisms (p, p') in striped of Schreger. Left third of figure shows alternative light(s) and dark (s') bands as seen by reflected light.

Longitudinal Section of Enamel

Longitudinal section of enamel, treated with acid, showing disposition of ranges of enamel prisms (p,…

Enamel is composed of fine hexagonal fibers which are set on end on the surface of the dentine and fit into corresponding depressions. Shown is a thin section of enamel and a part of the dentine. Labels; a, cuticular pellicle of the enamel (Nasmyth's membrane); b, enamel fibers, or columns with fissures between them and cross striae; c, larger cavities in the enamel, communicating with the extremities of some of the dentinal tubuli.

Section of the Enamel

Enamel is composed of fine hexagonal fibers which are set on end on the surface of the dentine and fit…

A pinion and spur gear meshed together.

Gears

A pinion and spur gear meshed together.

"Under Side of Head of Geomys bursarius, showing entrance of external cheek-pouches and sulcate superior incisors." -Whitney, 1911

Plains Pocket Gopher

"Under Side of Head of Geomys bursarius, showing entrance of external cheek-pouches and sulcate superior…

"Skull and teeth of Gray's Rat Kangaroo (Bellongia grayii). c, upper canine tooth. i1, i2, i3, first, second, and third upper incisors; pm, second or posterior premolar (the first having been already shed); m1, m2, m3, m4, the four true molars." —The Encyclopedia Britannica, 1910

Gray's Rat Kangaroo

"Skull and teeth of Gray's Rat Kangaroo (Bellongia grayii). c, upper canine tooth. i1, i2, i3, first,…

"The click barrel-ratchet R is set upon another larger ratchet-wheel, with its teeth pointing the opposite way, and its click rT is set in the clock-frame. That ratchet is connected with the great wheel by a spring ss' pressing against the two pins s in the ratchet and s' in the wheel. When you wind up the weight, the click Tr prevents the ratchet from turning back or to the right; and as the spring ss' is kept by the weight in a state of tension equivalent to the weight itself it will drive the wheel to the left for a short distance, when its end s is held fast, with the same force as if that end was pulled forward by the weight; and as the great wheel has to move very little during the short time the clock is winding, the spring will keep the clock going long enough." — Encyclopedia Britanica, 1893

Harrison's Going-Ratchet

"The click barrel-ratchet R is set upon another larger ratchet-wheel, with its teeth pointing the opposite…

The head of a crocodile, showing off its ferocious mouth and teeth.

Crocodile Head

The head of a crocodile, showing off its ferocious mouth and teeth.

"Side view of skull of horse, with the bone removed so as to expose the whole of the teeth. PMx, premaxilla; Mx, maxilla; Na, nasal bone; Ma, malar bone; L, lacrymal bone; Fr, frontal bone; Sq, squamosal bone; Pa, parietal bone; oc, occipital condyle; pp, paroccipital process; i, the three incisor teeth; c, the canine tooth; pm1, the situation of the rudimentary first premolar, which has been lost in the lower, but is present in the upper jaw; pm2, pm3, and pm4, the three fully-developed premolar teeth; m, the three true molar teeth." — Encyclopedia Britannica, 1893

Horse Skull

"Side view of skull of horse, with the bone removed so as to expose the whole of the teeth. PMx, premaxilla;…

"Skull of Hydropotes inermis (adult male), a deer without antlers, but with largely-developed upper canine teeth." —The Encyclopedia Britannica, 1903

Hydropotes Inermis

"Skull of Hydropotes inermis (adult male), a deer without antlers, but with largely-developed upper…

Illustrating the relationship of the lateral incisor tooth to the palatal cleft. A, Normal hard palate. The premaxilla is stippled; the lateral incisor occurs in the suture between it and the maxilla. B, Double cleft palate, the lateral incisor being situated on the premaxilla to the inner side of the cleft. The septum of the nose is exposed in the cleft between the maxillary bones. C, Double cleft palate, the lateral incisor being situated on the maxilla to the outer side of the cleft.

Incisor Relation to Palatal Cleft

Illustrating the relationship of the lateral incisor tooth to the palatal cleft. A, Normal hard palate.…

Incisor Tooth

Incisor Tooth

Incisor Tooth

Median incisor teeth of left side labial (A) and lateral (B) aspects.

Median Incisor Teeth

Median incisor teeth of left side labial (A) and lateral (B) aspects.

Temporary incisor teeth of left side. A, median; B, lateral incisors.

Temporary Incisor

Temporary incisor teeth of left side. A, median; B, lateral incisors.

Unworn surfaces of upper and lower permanent incisor teeth, lingual aspect.

Unworn Incisor

Unworn surfaces of upper and lower permanent incisor teeth, lingual aspect.

Horizontal section through both the upper and lower jaws to show the roots of the teeth. The sections were carried through the bones a short distance from the edge of their alveolar borders. The upper figure shows the upper teeth, the lower figure the lower teeth. Note the flattened roots of the lower incisors, the two root canals in the anterior root of each lower molar, and the confluence of the three roots of the upper wisdom teeth.

Jaw Showing Roots of Teeth

Horizontal section through both the upper and lower jaws to show the roots of the teeth. The sections…

Right half of lower jaw, with the corresponding teeth. The letters and numbers point to the various cusps or their modifications on the different teeth.

Lower Jaw with Teeth

Right half of lower jaw, with the corresponding teeth. The letters and numbers point to the various…

Right half of upper jaw (from below), with the corresponding teeth. The letters and numbers point to the classes of teeth and the numbers in classes.

Upper Jaw with Teeth

Right half of upper jaw (from below), with the corresponding teeth. The letters and numbers point to…

The bottom jaw of an iguana.

Iguana Jaw

The bottom jaw of an iguana.

Half of the lower jaw. Labels: a, the base; b, the angle; c, the ramus; d, the condyle; e, the coronaid process; h, the two incisors or cutting teeth; i, one canine; k, two small molar; l, three large molar or grinding teeth.

Lower Jaw

Half of the lower jaw. Labels: a, the base; b, the angle; c, the ramus; d, the condyle; e, the coronaid…

Lower jawbone with the teeth.

The lower jaw

Lower jawbone with the teeth.

This illustration shows an enlarged view of the mouth of a lamprey.

Mouth of Lamprey

This illustration shows an enlarged view of the mouth of a lamprey.

"The internal structure of the lion, except in slight details, resembles that of the other Felidae, the whole organization being that of an animal modified to fulfil, in the most perfect degree yet attained, an active, predaceous mode of existence." —The Encyclopedia Britannica, 1910

Lion Skull

"The internal structure of the lion, except in slight details, resembles that of the other Felidae,…

Lateral half of mandible of a rabbi, opened to show the arrangement of rodent teeth.

Mandible of a Rabbit

Lateral half of mandible of a rabbi, opened to show the arrangement of rodent teeth.

The inner aspect of the right superior maxilla.

Inner Aspect of Superior Maxilla

The inner aspect of the right superior maxilla.

Ossification of superior maxilla. A, outer side. B, inner side. C, under side. Labels: a, nasal process; b, orbital plate; c, anterior nasal spine; d, infraorbital groove; e, infraorbital foramen; f, anterior palatine groove; g, palatal process; h, premaxillary suture; i, alveolar process.

Ossification of Superior Maxilla

Ossification of superior maxilla. A, outer side. B, inner side. C, under side. Labels: a, nasal process;…

An outer view of the right superior maxilla.

Outer View of Superior Maxilla

An outer view of the right superior maxilla.

The lower maxillary bone, including the bottom set of teeth.

Maxillary

The lower maxillary bone, including the bottom set of teeth.

Superior maxillary bone. With it's fellow on the opposite side, it forms the whole of the upper jaw. Each bone assists in forming part of the floor of the orbit, the floor and outer wall of the nasal fossae, and the greater part of the roof of the mouth. Labels: 1, orbital surface; 2, facial surface; 3, alveolar process.

Human Maxillary (Upper Jaw) Bone

Superior maxillary bone. With it's fellow on the opposite side, it forms the whole of the upper jaw.…

Inferior Maxillary Bone (lower jaw). It is the largest and strongest bone in the face and serves for the reception of the lower teeth.

Human Maxillary (Upper Jaw) Bone

Inferior Maxillary Bone (lower jaw). It is the largest and strongest bone in the face and serves for…

Right superior maxillary bone, inner surface.

Superior Maxillary Bone

Right superior maxillary bone, inner surface.

The molar teeth of a human, horse and dog. The first image to the left in a molar tooth of a horse. Labels: 1, The enamel. 2, The ivory. 3, Canals for blood vessels. The center image is a molar tooth of a human. Label: 1, The enamel. 2, The ivory. 3, The cavity containing blood vessels. 4, 5, Artery and nerve. The image on the right is a molar tooth of a dog. Labels: 1, The enamel. 2, The ivory. 3, Cavity for blood-vessels.

Comparison of the Molar Teeth of a Human, Horse, and Dog

The molar teeth of a human, horse and dog. The first image to the left in a molar tooth of a horse.…

A molar tooth

Molar Tooth

A molar tooth

Longitudinal section of a molar tooth. Labels: k, crown; n, neck; f, fangs; e, enamel; d, dentine; c, cement; p, pulp cavity.

Molar Tooth

Longitudinal section of a molar tooth. Labels: k, crown; n, neck; f, fangs; e, enamel; d, dentine; c,…